The Reason Zenos.

[Nezerius]

I like you think he used his full power. He didn't and never clarified he did. He fused with Shinryu, not to give him any edge... He never once admitted defeat to us either even when he "died". He literally asked us if we'd kill the primal or bind or etc so on. He did not NEED Shinryu, he wanted to test the true power of his might and the will of a god and go beyond that vs the godslayer. While he may not have planned to come back how he did, he did and he's better for it. We defeat him though as the primal he was, not truly him as himself by ourselves.

His first line of text, after the Shinryu fight, literally states that "The hunter has indeed become the hunted." before sayings his farewell to "My first friend. My enemy"
He died. He didn't have a plan on souljumping to a different corpse. He straight out killed himself because his own power combined with Shinryu wasn't enough to defeat his target. The fact that you keep using "died", and seem convinced that killing himself was all part of some kind of master plan just shows how much you seem to have forgotten about the Stormblood MSQ. I'd suggest rewatching the cutscenes again.

Oh, and his question on if we were to kill or bind the primal was Zenos asking about the WoL's knowledge about the Echo.

We even were shown just how damned hard it was at the end of Ghymlet Dark but that was under control of another character even.... And even then when given the chance for Zenos to go against ElidiZenos, Eldidibus yeeted out cuz he knew he'd lose. Especially because Zenos is starting to understand just how powerful he CAN be, beyond his already godly power. He's also more skilled than Elidibus imo, not just using brute strength magic but actually smart when it comes to destroying someone or getting what he wants. He's vindictive if that wasn't already obvious with the death of his father and claiming his body back after taking several bodies prior.

We don't know why exactly Elidibus gave up Zenos' body as quickly as he did. So anything regarding that is pure speculation.

In the end... not every ending has to be this great empathetic tragedy like we get with Emet Selch or the warriors of darkness. They're nice, but they don't make "true" evil villains.

And how exactly does this change the fact that we'd still end up beating Zenos in the end?

Y'know, the thing you were arguing against? The fact that the only outcome would be him losing against us? Or do you still believe that Zenos is going to permanently defeat us?