I have seen video of Verlander doing them and they were not even to parallel....pretty bad squats in my estimation.
I know Boddy wants deep squats. I don't know about Cressey and some of the others. At least parallel is what I would suggest. First thing I would do would do a squat, going deep with light weight or even just the bar. If your heel is coming off the floor early (which is very common) ankle mobility should be addressed before trying to go deep with squats. I think everyone is going to have different limitations with squats. Getting good from and technique before throwing a ton of weight on there is key.
When I was helping to coach some high school kids I would watch these kids throw 300 + lbs on the bar, shuffle back and get a 4" bend....when I told them what they were doing was silly and not a squat I was labeled a "hater", haha. Just my opinion I would want deep squats, parallel or lower even if this means doing lighter weight. Range of motion in this exercise.