Consider some of the atrocities his camp committed did not directly involve him but having his accomplices function on autopilot. I'm talking about Demiurge referring to humans as bipedal sheep. Ainz's lateral thinking functions cohesively with his nature. It can be a plausible notion that the flavor text of the Yggdrasil game is taking affect on his personality.
If you compare this story to another isekai anime called Log Horizon, the game's flavor text slowly manifested their effects. Whatever is written in the game will come true. Coincidentally, Ainz's class is an Overlord which speaks for itself.
I don't think Ainz intends to be a villain. He is merciless to those who oppose him but only kills when provoked or the situation needs to have him dirty his hands. Dominion was not his motivation why he does evil. He does evil as a means to an endpoint.
Actually started Log Horizon a while back but for some reason stopped along the way, cant recall the reason why but the anime was really good and yes Demiurge actually the one pushing him forward with the plan to conquer the world, his main objective was to look for others like him but then Demiurge started bringing ideas which others thought was Ainz and he just couldn't back-out, the anime is fun and action packed but the last episode were he killed the kingdom champion was really a sad moment and also the way he mercilessly slaughtered those soldiers got me thinking the idea of him becoming a villain.
I get what you mean.
Here is the reason why I think Ainz doesn't intend to be the villain the way he is. He wanted to create a utopia where all beings could live in harmony under his rule, so any opposition should be eliminated. If you read the light novels, his rule of E-rantel which will be shown in Season 4, was a peaceful rule. While his undead soldiers occupied the city, everything was bakc to normal and demi humans get to walk in towns without being harmed.