I dont agree or disagree with anyone, but i have trained with full backs in Rugby that have never squatted with any great conviction yet as a matter of course for the sport, E.G. 40-100m sprints, they have good muscularity and can all squat more than 1.5x bodyweight regardless of squat training 'per-say'.
Oh and for the record by reading any true information from any eminent sprint/power coach, they will all confirm that the most influencial muscle(s)used within sprinting are the Hamstrings. So for any serious increase in sprint/power increases, the focus of any 'Leg Day' [Although personally I disagree with such a day and prefer to ultilize, A day for Quadriceps and Calve's Dominant and a second day for Hamstrings and Gluteals] (just a personal standpoint however), Should be The Hamstrings, utilizing the big exercise's, for example, the Romanian Deadlift and Good Mornings. Throw in some Plyometric work and whatever the goal, be it Power, Strength, Hypertrophy, or Speed, Such a training plan is effective on all levels.
M.J.Cartwright. Pontypridd South Wales.