I would only make 1 suggestion at this point for flying:
Have the mouse control the camera, not the cursor. Have the javelins turn a maximum rate towards the direction camera is facing until the javelin is centred. Having to constantly reposition the mouse on the mouse pad because it keeps readjusting the position towards the centre just doesn't work well. In the short term it's pretty annoying and long term will become a frustration.
Either implement something like the above or have the option to not have the game keep centering the mouse would be nice. A controller can keep a joystick held hard in one direction to make a turn without having to constantly reposition the stick - mouse control needs the same ability.
We previously had no auto-centering (in Alpha and demo) and the feedback since then with auto-centering reenabled has been overwhelmingly positive. Not everybody prefers this obviously but a lot of this can be mitigated by increasing flight sensitivity to decrease mouse repositioning. You can also increase mouse response to increase acceleration for more significant cursor movement with less mouse movement. I’d suggest continuing to mess with the various settings to see if you can achieve a feel that you like.