As you said in a previous post here, though, there is no way to really tell how much of that behavior was the character's human side. From the very first scene, it was clear he was unstable. The fist-slamming tantrum mode, in hindsight, reminded me a lot of Philia's ground-pound attack.
The game dialogue seemed to imply that sort of violence was a recent development, as an NPC in Wright describes a group of local bandits who previously lived in Eulmore, but were exiled after being caught stealing from the free citizenry. Stealing from the free citizenry, like Kai-Shirr was charged with fraud? That should have guaranteed a one-way trip out of a window, or a pound of flesh or five. But they were exiled and fit to rob unlucky travelers.
It also seems reasonable that there would have been more awareness in the city of such cruelty, if it were an ongoing regular thing. But there was nothing. Not even the other workers telling us "hey, be careful".
Then there is Amity--where workers fled cruel patrons, not Vauthry. Amity feared Vauthry would send the army there, but he never did.
The Derelicts uses tropey imagery, but the actual NPC dialogue doesn't back up the "poor" were actually poor. There's this guy:
At least two people are there to sell the fixtures and whatnot dumped around the city proper, one lady wants to get in to be a famous singer, a Viis from the Crystarium is there out of curiosity, one guy wants a "pretty partner" on each arm and fancy food. Wright and Stilltide residents further confirm "the hopefuls" left their reliable lives for a gambler's chance in Vegas. This was no enforced famine or such, Eulmore was still purchasing produce from the neighboring villages, mentioned by an NPC in Stilltide.
The Brume was a more genuine example of the trope they were trying to use here, imo.
The Minstreling Wanderer stated he couldn't say whether Vauthry was always like that. While it's nothing concrete, that they added this little extra bit of info made me wonder. No one in Eulmore referred to Vauthry as a "god", either, he was "a great man", with a vague gift to calm Sin Eaters. The god talk only began at the Exarch's visit.
I prefer to think positive, because of all the characters in this series with blood on their hands, this one in particular is held to a far more unforgiving standard, even though the game clearly showed he was compromised before birth, with a corruption literally no other character in the game was able to fight.