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

[Lauront]

Than why did she even write him?

If the character stimulates you to think about things in a certain way, or gets a certain reaction out of you, they can act as a useful writing tool in that way. I am no writer, and I can't say I am a huge fan of him or even the intended (?) messaging behind him (other than "grow up and stop being so self-centered if you want your one-sided best and first ever hostage friend to notice you"), but I appreciated Zenos in that sense in EW. I think she was aiming to prompt some 'deep thinking' with Hermes but he was under-developed, the civilisational backgrop against which they were trying to demonstrate these points was poorly suited to it and so it came across as relentlessly pretentious and self-indulgent. At least in my eyes.