I first played MCC on 10 to adjust to the 60fps and have slowly lowered it to 8 as I find that's optimal. Also, I would argue that in alotta situations, my higher sensitivity has saved me in close quarters fights that require quick turning etc. So the reason for "pro" players to use a lower one, I don't understand
Consistency, you don't use something that helps 10% of the time, compared to 90% of the time. You can't out strafe a 4 setting so there is no reason to really go above it, is why use it. Pro's also don't "just have people behind them" they communicate none stop so they don't find themselves turning around, they generally keep all the action in a front of themselves.
Still to this day, i've only meet one person I would call good that plays above 7.
I'd be wining to bet, if you lowered to around 4, played more mid range fights with the BR, your win ratio and K/D would drastically improve.
The argument for needing a higher sensitivity for turning around or close quarter combat shows a players ability. Drop it to 4 and force yourself to use the BR, you'll be better than you ever were in a few days.