IIRC, you're a young, skinny volleyball player. The general population, particularly those who are older and fatter, will have to needlessly work much, much harder to achieve "ATG" depth. "ATG" depth can only be achieved by relaxing the hamstrings. So, while it is true that the quadriceps and glutes are trained over a longer range of motion, the hamstrings are not trained to the same degree. "ATG" squats also take a tremendous amount of weight off the bar making them less effective at actually getting strong. I find that people who talk about "ATG" squats all squat to variable depths. "ATG" doesn't mean anything. It is not quantifiable. As for the stretch reflex, perhaps you can get a stronger bounce, but that is because most people who squat "ATG" literally bounce off of their hamstrings colliding with their calves. Not quite the same as making full use of the hamstring muscle's stretch-shortening cycle as taught in the SS style squat.
In the context of the SS Novice/Intermediate programs, "ATG" squats do not make sense. They do not make sense for competitive powerlifters either. Those two groups make up the majority of the population on this website. That is why "so many people are against them on here". Perhaps they have sensible uses in the context of your program and your goals.