<Snipped quote by Cyclone>
To be fair, his description of Vulamera isn't entirely wrong. It's a little extreme, but she IS arrogant and prone to prattling
She's not really bad, just not very likeable xD
Zephyrion really isn't stupid and for the most part he doesn't lie or act outright evil.
He's just very judgemental, very opinionated, very quarrelsome, very open about how he doesn't hold himself to the same standards as others (but you still can't call him a hypocrite!), very loud once you've got his attention...
In this case I'd say he's justified in his loathing of her. I actually lean towards him being in the right, because since the start and for next to no reason Vulamera has always been condescending and hostile to him. In addition she demonstrated no good reason for him to think she's actually that intelligent, so she falls into the trap of the other gods that he sees as inactive and useless.
Granted if Zephyrion was a normal person he might just turn the other cheek or try to be nice and make amends and therefore prevent the mutual hatred from escalating as much as it has, but his personality isn't like that.
So of course he's right.