there are thing mouse players can do that controller users can't… like play outside of the intended range with precision weapons, and turn instantly etc.
the sum of these imbalances is that your are able to contend with the caliber of player you are contending with.
The issue I have is
how controller players are contending with MnK players. The advantage controller has with aim assist is way more applicable and constant than the advantages you're saying MnK has over controller.
The benefits of being able to instantly turn are almost completely diminished in a game where fights on average last longer than two seconds, flat out. As for shooting outside of a weapon's intended range, this (in my experience and I'd find it hard to believe otherwise) again isn't an issue 99% of the time because most engagements are within aim-assist ranges anyways.
To be clear, I can acknowledge that most of my gripes are centered around Ranked play and 4v4 modes in general due to map size. I am sympathetic to the edge-cases where MnK can be more dominant than controller but they are very much just that; edge cases.
I dunno how controversial this would be but I'd advocate for a single shot, 5sk weapon like the H5 magnum or DMR to be the starter weapon in Ranked instead of the BR. One of the biggest issues right now with mouse is how often you miss bullets within a burst due to the insane strafe speed, and missing even one bullet can massively increase the TTK of the BR. Only having to hit a single shot center mass would help a lot in leveling the playing field and tbh I just find single shot weapons to be more skillful anyways. I doubt it would happen but it at least would be an easy change.