Did Zenos ruin Endwalker

[Gemina]

Have him hunt down and kill everyone precious to the WoL since the body possessing thing adds the possessed's memories as shown by Lahabrea in ARR.

He was on his way to do that in Garlemald. The WoL stopped him despite occupying another body and having the odds heavily turned against them.

Take Zodiark's power for himself after Fandaniel is killed. Hell, change history so that he unwillingly becomes Zodiark's core after deciding to wipe out mankind to have his fight with the WoL on a mountain of corpses.

He planned on doing this as well prior to Fandaniel taking Zodiark for himself. Zenos planned on taking everything away from the WoL because he wanted their unbridled rage turned on him as they fought on a pile of ashes. Remember? If this actually came to fruition, there wouldn't much of a game left to play.

Not have a solo instance that unlike Varis doesn't even get an Extreme version that could have acted as a gateway to an exploratory zone.

This fight was always going to end in a solo instance, and because it is MSQ the difficulty wasn't going to be road blocker. You don't have to like it, but Zenos being an 8-man encounter doesn't fit the narrative that was set for his character. That was the Shinryu encounter back in SB.

Do something with the fact that he's the grandson of a damn Ancient. Add the damn side story to the game like everything else they should have as A) I ain't reading all that otherwise as it doesn't matter and B) it would have salvaged him at least.

Again. Like what? It is perfectly fine that how well Zenos was done as a character is subjective. No one is going to get anywhere trying to convince those who hate him to like him, and those who like him to hate him. And they actually did do something, now that I think about it. His grandfather built Garlemald and the imperial army. The grandson reduced it to ash. Both happen off screen.