Regarding Sabo, Ace and Luffy

I've seen perhaps one or two individuals support the notion that Sabo is Ace's sloppy patch, despite it not being a very popular notion. Nevertheless, I'd like to argue against this opinion on Sabo's behalf, whom I believe to be a unique and interesting alternative to the brother dynamic to which we were introduced prior to Ace's death. I fully understand why some may argue that Sabo is a discount Ace, but I see it as an insult to the struggles Sabo has been enduring resulting from the guilt Ace's death has evoked. Sabo offers us a twist on the theme of brotherhood reinforced early in the story; thus, he is a fresh character who can hardly be labelled as a 'cheap patch'.

Before we were aware of Sabo's existence, Ace and Luffy seemed to be the complete pair, the original two. I never actually surmised that there might have been a third due to a lack of foreshadowing on Oda's part. However, as amusing as it sounds, this lack of foreshadowing served the story positively and added to the new dynamic of which I spoke earlier. Now, the question is how Sabo's abrupt appearance befits the theme of brotherhood post timeskip. If you recall, both Ace and Luffy supported each other following the supposed death of their brother. The loss pained them both greatly; the two were almost literally inseparable as they worked tirelessly together to overcome their mutual pain and guilt. However, none of this aspect of their relationship was witnessed prior to the timeskip (excluding the flashback, where Ace was already dead). This was, in my opinion, all for the better considering the fact that Luffy and Sabo's post timeskip relationship was shaped by similar circumstances; the two love and support the other unconditionally as they both need one another to move forward from the passing of their beloved Ace. This aspect of the overall theme of brotherhood is much more fleshed out and nuanced than in pre timeskip One Piece, where Sabo's existence was unbeknownst to us all and Ace and Luffy did not seem to be recovering from a scarring incident. Furthermore, the Ace and Luffy dynamic differs highly from the current relationship between Sabo and Luffy; the latter is new material meant to develop Sabo and Luffy as characters. It's really not a cheap patch, it's completely different.

Sabo is being developed differently than Ace. We did not witness Ace's growth as a character resulting from Sabo's apparent death; once again, this is completely new material. 'Sabo's Adventure' in the Dressrosa arc highlights the guilt Sabo felt (and still feels, mind you) upon failing to come to Ace's aid. Imagine recovering the memory of a loved one shortly after their death. Sabo evidently feels responsible for the incident, hence thanking Luffy for living. Luffy feels responsible as well, and thus, the brothers are forced to support each other mutually to recover from their loss. What Sabo is experiencing has not been presented to us by Ace.

Ultimately, Sabo is his own individual, regardless of which attacks he uses. On the topic of the Mera Mera no Mi, however, I believe that Oda intended for Sabo to carry on Ace's will for reasons pertaining to the Will of D, though I have no idea if this will even be relevant in future reveals. I'd also find it interesting if Sabo turned out to be a D; unfortunately, this is unlikely considering the complete snot of a father he lived with.

TL;DR - Sabo is not Ace. He is Sabo.