I think both Eren and Ymir wanted the Rumbling.

I may be very wrong in this, so please feel free to correct me. This is just another interpretation of mine after watching the anime 4 times and browsing this subreddit and other AOT subreddits for hours.

It's shown to us that Ymir lived 2000 years in paths. But these 2000 years were earthen year. Time flows different in paradise, and hence, for her it was probably millions of years.

Now Eren says to Armin that Ymir loved King Fritz, which is probably true, but you can also love someone and hate someone at the same time. Hate accumulated over millions of years is not something that can be ignored. Being trapped in that hell hole, creating Titans tirelessly, never actually being able to live. She probably also wanted to destroy everything, but couldn't since she was bound by King Fritz's order. Her titan that layer split into nine titans probably also carried this hatred, mainly in the Attack titan, which Eren inherited.

And this Attack Titan largely influenced Eren's emotions. While he was already a violent person who sought freedom before anything, the Attack Titan made him more vicious. This was probably because Ymir's hatred was being channeled through the Attack titan, which also resonated with Eren's emotions. I think Eren mistook those emotions as his own as well, and called himself an idiot with an unsurmountable power.

When we talk of this bootstrap paradox in AOT, that nothing can be changed, and it's all fate, it kind of makes sense but not completely. It makes sense if we take Eren as a victim of his power or an Anti-hero who had no choice. But constantly throughout the Manga and Anime, it's been pointed out that Eren wanted this. Especially when he talked about killing his enemies over the other side. While it was also true that Marley vs The Paradise was inevitable, he truly wanted to destroy everything because it did not align with his idea of freedom. The idea of freedom that Armin showed him. The idea of freedom on which he was drunk to survive those years of hardships in the cadet corps and then the survey corps. The bootstrap paradox might be true, but that doesn't eliminate the factors to his paradox, the main ones being that Ymir wanted the Rumbling, so did Eren.

Also, when Eren freed Ymir, I think he actually sympathised with her. Ymir wanted the love she never got. She was never free. Eren hated those who took others' freedom. He freed her, and Ymir seized the opportunity to take her revenge. No matter how kind you are, time can change everything. After those millions of years she was probably so tired she did not care about anyone.

Also, I still don't understand completely as to why Mikasa had to be the one to free Ymir completely of her obsession with King Fritz. I think this was completely Eren's doing. He was, I think, able to manipulate the events to atleast some degree, and made it so that Mikasa killed him. But the major reason that I think he wanted to be killed by Mikasa was because he loved her. He loved her, but he was too stuck up doing other things that he himself wasn't aware of his feelings. But he realised it later, despite Mikasa's answer.