I played MWO with KB/M, it's pretty easy to get used to. If anything, the mouse precision aiming makes you more competitive, probably.
The core gameplay is fine, but the balance/meta gets in the way, and the devs were pretty slow at fixing things (while breaking new things, or introducing new unnecessary obtuse elements like ghost heat without detailing in the actual game how it would work - you had to check out details online).
But ultimately, after playing a lot of War Thunder tanks on realistic/simulation, I can't get back to this type of gameplay, it's too arcadey (and yes, I realize some other mech games are even more arcadey). I wish someone would make a mech sim that would really make you feel like you're really piloting a lumbering bulky metal beast, in the way War Thunder does it so well with tanks. It's weird to say it, but War Thunder tanks feels like a better 'mech' game than MwO.