The real question is how much is the stress switching to the glutes and hamstrings as you go deeper. What are we trying to train. If you want more glute and hamstring activation go deeper. I am actually concerned the squats are not hitting my quads enough. We have all seen people doing massive squats with no leg development
I will say this since I started squatting again my appetite and weight have increased
I read many times that the squat is the best all around exercise a person can do. I think you have to do some additional exercises if you have hard to develop quads.
When on long drives and I have to stop for gas, I jump out of the car and do a couple of sets of bodyweight squats. I always feel invigorated afterwards.
-Can't give advice on developing big muscular quads because I've never managed to develop them. The biggest they've ever been, if I remember correctly, was 26" and that was when I weighed 225 lbs.
Leg extensions are fun because you can see all the cuts in your quads while doing them. I'm not sure they do much for growing them.