On The Topic Of Common Sentiments I Disagree With

Fair warning here, but I am an Anime-only who has only watched 2 seasons with some knowledge about the most spoiler-y controversial moments later on. With that in mind, what I am going to say is going to apply to the anime only and I am not going to comment on the manga directly. So, the sentiments I am responding to would be more general or about things that already happened in the anime and not about specific points only in the manga.

Sentiments I disagree with:

1.The Main Plot is About Aqua's Revenge

From where I am standing currently, it seems to be much more about the social commentary on the entertainment industry and Aqua's revenge is just his relation to said industry. Think about it. Every named character has at least some connections to the entertainment industry and often has an arc that connects to it. Every storyline has featured the entertainment industry in some way(including the short hands I have seen for future arcs). Even Aqua's revenge has several points of connection: Ai's death was directly caused by entitlement idol fans have that the idol industry set, Aqua uses his acting/connections in the industry as tools for his revenge, and Aqua's father has connections to the industry that is being traced. Meanwhile, Aqua's revenge itself has very little relation to all the other plots that focus on the industry more heavily and they sometimes basically have no relation as Aqua himself often gets sidetracked about his own revenge with his mind more on helping those around him than progressing his revenge goal. A lot of my favorite parts of the anime have basically no relations to it (i.e. Ai's prologue characterization, Kana's and Akane's rivalry, Abiko's and Yoriko's verbal fight, Yoriko's cry of relief seeing the end of Sweet Today, Abiko's characterization, etc).

2. Kana Is Plot Irrelevant

Sort of related to the first, as Kana's character is very much about her old child star days and the lingering effects that had on her mentally. But even when taking Aqua's revenge as the main plot, Kana's irrelevance is her relevance theme-wise as silly as that sounds. I think what a "light" is in relation to Oshi no Ko is greatly misunderstood. The light isn't an escape that completely saves you from darkness, but a break that entertainment often provides. Ai for a lot of characters in the story is a light, not because she fixes their problems/darkness, but because she is a much-needed break from their darkness(especially for Serina/Ruby). Kana works a similar way, but moreso on a person-to-person level for Aqua(not as a star). Kana is a light for Aqua because she is disconnected from his revenge and her honesty as well as lack of relevance to said revenge allows him to relax from it(season 1, episode 8 basically implied as much about her honesty being relaxing to Aqua). And Aqua's revenge plot is about a lot more than just progressing to the revenge goal too, btw. It extends to the tragedy of him choosing to miss out on enjoying life due to his hyper-fixation on revenge that works to make him believe he doesn't deserve to enjoy life(season 2, episode 13). His revenge also stops him from hoping for a future as he expects his future to end afterwards and doesn't want to take anyone with him(season 2, episode 11). Where Kana fits into this is as the one-person who he can being his old, non-revenge self around and allows him to put his walls down to just enjoy life.

3. Akane Is A Plot Device

Akane adds too much character-wise in the plot, both for Aqua's revenge and the entertainment industry for her role to be reduced to that. Akane is obviously related as she is the comfort in the dark for Aqua, but she tends to figure out things way after we already knew or alongside the audience from other characters. Plot-wise, Akane's plot deductions are easily replaceable with Aqua's/Taishi's inner monologue(i.e. the moments after Aqua's PTSD attack) or trust in the audience to get to the implied conclusions about the answer which could've been put together later by Aqua himself(i.e. why Aqua didn't piece together a loophole during the bridge scene). Akane's deductions aren't the main things she is adding to the plot imo. Instead, what she is adding a new character dynamic into the mix that tests Aqua as a character further by getting directly involved as a helper causing her to reveal more about herself and him in the process. Akane allows Aqua someone to lean on in his darkest moments which allows us to see how he reacts to that unconditional support(guilt-ridden, appreciative, and self-conscious) and sides to Akane from her reaction after finding out(empathetic, enabling, and kind).

Akane does the same for the entertainment plot. In her introduction arc, Akane was a personal character dive into Reality TV as a hated contestant, judged for a single bad moment that she did out of overwhelming staggering pressure during a moment of emotional weakness that didn't truly accurately define who she is as a whole person. Akane, then from there, after everything was settled, learned to put up more walls between her and the audience in order to not be hurt in the same way again by hiding her more vulnerable self to be for only those she is close to and using an Ai persona on the front stage. Akane addition to the entertainment plot is to showcase a type of personality especially vulnerable to that reality tv environment(shy, quiet, self-conscious, genuine) as well as its effects on said person after learning from that experience. Akane's character also adds to the entertainment plot through her connection of a fan to her art form, an observant, analytical empathetic person that looks deeply at a character as a fan of the work and then channels that fan love through her art of acting. This fan love is also what connects her to both Kana and Ai. Her love as a fan inspired her to act through Kana and also through Ai, who she uses to inspires more confidence in herself through physically emulating the style of Ai in her day to day life as well as a figure that still helps get her through online performances. In other words, I see Akane as the power of a fans that use it to make art of their own and the type of person who introvertly hermits herself to art she enjoys as the main additions she adds to the entertainment industry plot.

4. Kana is Just A Typical Tsundere with No Character Development

That describes so little of her actual character and doesn't even completely accurately describe her relationship to Aqua either. Kana is essentially is a dive into the psyche of a child star grown up. Every personality trait that she has, you can essentially trace back to her times as a child actor or as a by-product of the after effects. Her rudeness and melodramatics isn't there to tick trope boxes of a tsundere, but because it was an active writing decision made to reflect the fact she was overly pampered by the adults around her, allowed to say and act however she wanted with no real parental guidance (something made apparent in the first episode when almost all the adults comforted her after her temper tantrum). Which is the main reason why those traits became a core part of her character even in the present. It's also worth noting that she is a more of a brutally honest character in most of her rudeness, which is significantly different from the typical tsundere whose rudeness is an act to hide feelings.

Another sign that these traits weren't just there to be Tsundere traits is the fact the character grew an identity more complex that didn't cleanly check the boxes of one. She, after, in that same introduction episode 1, learned from the director, Taishi, that this was going to negatively affect her career later if she continued to be so rude and arrogant, so the next time we see her in future productions(Sweet Today and Tokyo Blade) she does act sociable enough to get along with her co-workers(outside of Akane). Moreover, she did genuinely learn to appreciate the work others put into the production by thinking outside of herself from her childhood convo with Taishi in the first episode. Now we see her commenting positively on Aqua's first attempt at acting in Sweet Today, sympathizing with Yoriko's(creator of Sweet Today) plight during the production, learning tips from Taiki during Tokyo Blade, and helping Melt improve his acting in Tokyo Blade. Additionally, she is now more self-conscious after her fall from grace poking fun of herself frequently and even developing a complex about her foul mouth(season 1, episodes 9-10). Again, her personality and actions is informed by her background as a child actor and not there to be a simple trope-y love interest.

Why doesn't she ask for help about her personal struggles to other characters when she is having them? Because after she was no longer big, everyone, including her own family, left her, so she got used to isolation and handling her issues entirely by herself.

Why doesn't she tell Aqua her feelings for him? Because he is dating Akane so she was waiting to see if they would break up the work relationship to confess(hence why she was so antsy about it during the entire second season and advised Aqua to give Akane a real answer soon during episode 11), only to not long after find out they are now dating for real. Kana, so far, hasn't really gotten a real chance to confess due to outside forces(her being an idol and Akane dating Aqua).

And I mean I could go on to explain every trait of hers, but I think you get the point.

There are tons of other common opinions that I see around the fandom that I disagree with as well, but this was getting rather long, a lot longer than I expected, so I'll leave it for now.