I've had no problems flying with keyboard and mouse, just took a little getting used to at first as it always does when it comes to games vehicles in the air.
And I really don't understand how it's possible for there to be so much raging over the mouse being inverted.
Do you use inverted mouse normally and you're able to adjust to the opposite just for the air vehicles?
If so you must be more mentally flexible than most of us inverted mouse users, I've used inverted Y axis for the MWLL ground units (and every other FPS and Flight Sim game going back as far as Doom), and the difficulty is having to think in reverse when we jump into the air vehicles (forward is up instead of down, which goes against the brain thinking of how you would move a real flightstick on a plane).
Understandable that this might have been missed during development if none of the devs or testers are reverse Y axis users, but I'll look forward to a fix someday, until then I will stick to ground units.