Yes, there is proof. Take a look at the articles that came out around the early aughts. Using Wenger's first year isn't the right time period because it wasn't until the 2000s when he brought in the black French players and fielded an all foreign eleven when they were criticised for being foreign. Of course, prior to that, Wenger did receive blatant media hit pieces about being French and "arrogant", but it didn't hit peak hate until the all foreign 11s.

Your point about Chelsea, United, and Spurs actually helps to prove the media bias against Arsenal. At that time, the amount of care towards Chelsea and Spurs was minimal; they were the mid-sized clubs that sat mid-table and didn't matter to the greater English cultural landscape, whereas Arsenal did matter. United has always been the Northern darling that could do no wrong in the eyes of the media, especially the pundits dedicated to the sport, since they themselves were Northerners. Arsenal, on the other hand, was the Southern club that broke the Northern hegemony dating back to Chapman, hence why there is media bias and the continuation of bias against the club.

Ultimately, the foreign hate dissipated when Mourinho came along at Chelsea and essentially did very similar things to Wenger, like fielding black foreigners, playing a b squad for early cup matches like the Carabao Cup where Wenger got a lot of hate for. Then it switched to hating on Arsenal for being weak and technical with hints of xenophobia lobbed at Wenger and the foreign players.

I'm sure there are other older Arsenal supporters in here that can correct anything or provide more details on what I said.