This exactly!!! Just have a look at Kerbal Space Program for "Ultra realistic" or better at I-War/I-War 2: Edge of chaos for a good representation of newtonian flight model, nerfed just enough to make it fun to play in a game.Speed in any axis is cumulative - the longer you apply thrust, the faster you fly, roll, yaw or whatever.
This is how normal objects behave.
Does your ship behave like a normal object when flight assist's supposedly disabled? Because mine certainly doesn't.
F=MA, P=MV, KE = MV^2, unless you're playing Elite Dangerous, in which case all that goes straight out the window.
ED doesn't fly properly - doesn't even spin properly. If anything, the only thing spinning is a large wooden box 6ft under Westminster Abbey.
Flight assist should be re-labelled with 'low' and 'high' settings, instead of on or off.
E: D is definitely NOT a simulation of accurate newtonian space flight mechanics... more a mix between Elite II: Frontier and Wing Commander