What's the point with that quite lackluster story in Endwalker?

[Vyrerus]

But I also didn't really like how the situation was setup or how nothing came of it.

I know you're talking about In From The Cold, but this sentence really does apply to pretty much every major story beat in Endwalker for me.

But also especially to that quest, because legitimately it was just a thing that happened. Zenos didn't use our body for anything other than a menacing stroll. We didn't seem to really learn anything by piloting the Garlean's body. There were no references or tie ins back to it, as of yet.

Some theory crafting in and around the whole, "Soul Supply" section of Solution-9 does have some thinkers thinking, but theory crafting generally trends towards mostly inaccurate, given our writers'/devs' love of expectation subversion.