In the prone position you tilt the rifle to the side and the ever operates quite easily
So you have to take it off your shoulder and lose your sight picture.
Nope, you do neither. It takes practice, but once you have mastered it it works very well.
In which case you have an absolutely crap prone shooting position, compromised by the need to twist. If you don't take the rifle off its position on your shoulder while maintaining your sight picture that means you have to lift your shoulder to twist the rifle which means your position is not as stable as it could be.
It also means you lose your body position. And of course it's obvious that one doesn't aim a weapon, one aims one's body and the weapon follows.
Too, if it takes practice it's not easy. There's a word for that.