Forward-backward thrust (main) is fundamentally different from vertical and horizontal thrust (strafes). If you press and then release the forward thrust button, the speed you have gained will be maintained. But if you do the same with the strafe buttons, the ship will start to slow down after you release the button.

For control, I use a configuration of two joysticks (HOSAS): the left one for rotations, the right one (Omni-Throttle) for thrusts.
1) When using the joystick for the main thrust, the maximum speed of the ship will depend on how far the joystick is deflected (at full deflection, the maximum speed will be 300 m/s - it is impossible to accelerate further). But if you quickly move it to the central position, the ship will not drop to 0 m/s, but will continue to fly with the speed it has gained.
2) When using the joystick for strafes, there is no relationship at all between the speed and the degree of deflection along the axis. That is, in this case, using the analog axes of the joystick is no different from using the keyboard.

You expect that the degree of deviation along one or another analog axis will affect acceleration, but not the speed itself. This also slightly breaks the meaning of using the direction lock button.