After seeing the full extent of the Founding Titan's power, I'm left wondering if Eren truly utilized it to its maximum potential. Could he have brought back past shifters to fight for him permanently, or maybe even altered Eldian biology beyond what we saw? There feels like there was more to unlock.
He pretty much did everything. Controlling ALL past titans and influencing generations? That's peak. What more could he even do without breaking the universe?
Maybe he could've 'un-titanized' everyone without dying. Like, a full reset of all Eldians back to normal humans. That would've been a true ultimate power move.
I think the 'more' was limited by Ymir's will and the paths. He was using her power, not creating it. So, whatever she could conceive, he could do.
He could've created an army of intelligent, loyal titans that could speak and strategize. Instead of mindless followers, imagine a true titan force!
He used it to achieve his goal. Any more power would've just been overkill or irrelevant to his mission. He was already basically a god.