That boosting to max speed and then switching flight assist off thing is a bit of an exploit. I wonder if they will find a way of stopping this.
I havent had any problems boosting away from an interdiction without switching F/A off yet and that is flying a sidewinder, a hauler and a lately a Lakon type 6. I just make sure engines are on max and the moment I come out of supercruise, I boost.
The game is clearly geared (at the moment) so we can get away from faster ships as long as we are prompt. If it wasnt, then every interdiction by a sidewinder would spell doom (for me) as the 'fighters' would catch the 'haulers'.
Having said that I have taken to switching F/A off now at these times... because I can.