Is "Paddy Wagon" racist? Was the bottle of whisky at the violent, drunken Leprechaun's foot (since removed) racist. Were the sub-human, monkey man cartoon depictions of Irish people in newspapers across the country racist?
Here's a good example from: https://www.irishtimes.com/culture/art-and-design/apes-psychos-alcos-how-british-cartoonists-depict-the-irish-1.3149409
English-Americans said of the Irish, "An Irish person is just a [defamatory slur for black people] turned inside out."
Boston are had many key events in American Revolutionary war so I Think the deserve to use the name patriots. All I can remember about DC is them deserting the city and letting the British burn it to the ground during war of 1812.
American society's relationship with Native Americans and its use of their culture is a distinct issue. It's akin to why no team in the Bundesliga is named the "Shofars": namely the Soviet and American armies. Instead of getting executed for international war crimes, our perpetrators of genocide got memorialized and their victims got made into mascots.
In a broader sense, racial/ethnic/religious /socioeconomic based humor is now dead...the Trevelers, Celtics, and organizers of the Hillbilly Classic just haven't gotten the memo yet. I say that with a bit of wistful sadness. I have heartily laughed at and made (bad ones) such jokes. But humans being what they are, those types of jokes are always tainted by the inequities of power. And that is corrosive. Someone is always being laughed at in such jokes....not laughed with. You can argue that is a core element of humor (and I would not disagree). I suspect after the first fart joke: https://www.reuters.com/article/us-joke-odd/worlds-oldest-joke-traced-back-to-1900-bc-idUSKUA14785120080801 the second joke was about someone being different.
But, I think, we can evolve to be better. Sammy Davis Jr. had to do a routine every night in Vegas with his "friends" Dean Martin and Frank Sinatra where a chunk of the jokes were about Sammy being black. Most of those jokes were only "funny" because America was racist...and the joke was that Sammy was nevertheless allowed to be on stage with them.
There is, of course, lots of nuanced ambiguity. But mascots, team names, and theme nights, are probably poor places to have fun with that ambiguity.