Mix the mouse with the keyboards, for heaven's sake... "Be creative", as someone said.
In combat I don't click much stuff, only those I don't remember the mapping or aren't worth mapping, anyway.
You can still man flaps, gear, guns, pitch, throttle, view, radiator, can of beer & co. with keyboard all the time.
But uncaging the artificial horizon, for example, is something you don't need to assign a key to, but you might still need to do it sometimes, so it's better to be able to just look, click/turn it instead of remembering LShift+LCtrl+RAlt+U+H or something like that.
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