To be fair, there was really no way for Erenville to know just what Alpha actually is. I mean, he's a chocobo... but he isn't? Honestly that stuff is rather confusing, and the Omegas didn't really go over that all too well aside from reassuring us that Alpha did indeed have a soul and is a person. I think my personal favorite part is when Erenville resolved to not tell his Sharlayan compatriots because he feared they may treat him poorly to attempt to discover just what he is. That was pretty considerate of him.
The "eccentric" part was probably another Azem nod, to be honest. As for the faith, well that's actually one part I think Shadowbringers could have improved upon. Instead of Elidibus cosplaying as a Dissidia NT character (and really, what's with the model rips anyway? What with that and the Cloud of Darkness from NT Eden sure did like copying stuff), it would've been a pretty tense situation to see the Emissary instead use Eorzea's faith in us in particular against us in the worst of possible ways.
I think it might've been easier to get invested in Erenville as a character if he had gotten more screen time. We really didn't interact with him all that much in Endwalker, and it made it difficult to really get a feel for his character. I feel the Warrior of Light spent the most time in Thavnair and Elpis by far in the MSQ to be perfectly honest. Garlemald, Sharlayan, Labyrinthos, and Ultima Thule all felt really short as segments.
I don't know, it honestly read more to me like Erenville always planned to make an odyssey of himself but got caught up in the work that suddenly became much more dire due to Sharlayan's abrupt revelation about the Final Days. It's a little like what Cleretic said here:
It's more to me like Erenville was on the "good guy's side" from the start, in that he fights for the little guys. It makes sense, and I'm glad the Gleaners have someone to fight for them since it did feel more than a little bit like they had been being mistreated and taken advantage of by the Sharlayan higher ups.
Wait, where did you get that idea there are only two empty slots left on the site?
Also, I'm not entirely sure we can even GET Viera culture from Erenville. He honestly comes across as more than a little sequestered and I wouldn't be surprised if he possesses little to no actual knowledge on what Viera culture is like.