Reiketsu

Almighty is far and away number 1. The MEoDP requires actual contact; the Almighty has no such limitation and change the future to whatever Yhwach wishes. It's so overpowered that the author himself had to actually nullify it for the heroes to have a chance to win.

Uhh... there was a HUGE reason for Goku not using SSJ3: it has a MASSIVE (read: prohibitive) rate of power consumption.

The IRL reason: the hair was a massive PITA to draw (let alone animate).

I have a feeling that Isayama would screw Eren and the ending up if he had another go at it.

You cannot turn the protagonist into a detestable (his words, not mine) villain in the final act after years irl of them being one of the most loved characters in manga. Even even lampshades it himself: He was an idiot granted overwhelming (nearly all-compassing) power. Despite that and becoming drunk with power, he remained true to his goal of protecting Paradise.

Also, Founder Ymir was the sole person to wield the totality of the Titan power, meaning that she had the Attack's ability to see the future. Eren was being manipulated by Ymir's 4D chess as much as he manipulated Grisha, Zeke, and to a lesser extent, everyone else.

Indeed. Imu's appearance is to set the tone for exactly how OUTCLASSED the Straw Hats (and honestly, EVERYONE else as well) really are. That was the narrative point of Imu's mysterious ailment after leaving Mary Geoise: He's on a timer, limiting how much damage he can realistically cause in the grand scheme.

The Straw Hats are going to have to take the final battle to his doorstep to be rid of him for good, and the current showing illustrates they are NOWHERE CLOSE to being ready for that fight, even with Loki's absurd battle power contributing as well. Hell, Rocks outright admitted that he could do nothing to Imu, and Luffy is weaker than him currently (and Shanks, at least in terms of SK Haki utilization).