In early years, my daughter had a teacher I liked a lot. Every time she used to complain about something not being fair she used to say: well, yes dear... life's not fair. 😉
I think we are complaining on a very high level here and realistically this won't ever be completely fair for everyone. Even on console you got those playing with mouse and keyboard, playing with extra long sticks, elite controllers, on huge TVs and on potato TVs on regular Xbox VS One X... can't control all that. And if PC is so unfair, there's no way you can argue this to be different when playing against some kid on his One S with some 20 year old TV leftover from his parents bedroom. And let's not forget that there are different PCs out there as well and the majority doesn't handle 240 Hz and whatnot.
Ive seen console players running circles around me, stomping me into the ground just as well as really good PC players.
If this is about mouse and keyboard, go ahead and allow it on Xbox as well. Give them a 60 FPS mode on top of that and remove cross play opt out altogether to be done with this topic.
Personally I think that the crossplay functionality of some Microsoft titles is absolutely fantastic.