Ok so I completely eliminated the throttle from the system, eliminated the mapping in game and even unplugged it from the joystick. Same thing.
Even if I use the keyboard buttons to fly, the 2,4,6 and 8 from the numpad, when going full left and full right, up until 50% left or right, the movement is very slow, then its sudden to max, comes back again fast, and when it gets to about 50% to center, it slows down a lot and moves slowly all the way to 50% the other side, then fast to max.
Im beginning to think that this is how the game is actually coded, with input filtering of some kind for the larger planes, since for very small ones there is no delay of this kind.
Tried the throttle leavers as well, when I move them fast to max, I can see the ingame throttles advancing slower.