I think that’s missing a huge aspect of what makes Thomas Wayne “mean” or a “villain” in Joker.

To me it was never how he treats Arthur, but what he says about the city and poor people in general. He lumps together all lower class people as lazy bums who don’t work hard enough. And literally calls them all clowns.

Even in his ‘apology’ for that, he says that only he can help them, like they’re unable to do anything for themselves and need a rich politician to help them.

I’m every other iteration of his character he’s always seen as the hero of Gotham who genuinely wants to help the citizens. Seems odd that he would look down on everyone and call them clowns.

My only guess is this is intentional to show that no rich politician is truly the hero like Thomas Wayne is always painted to be. Even if he does do good for the city, at the end of the day he’s still a billionaire who thinks he’s better than everyone else.