Isometric training effects on speed
I believe that all sports are dynamic. Based on this theory it makes sense to train dynamically if you want to increase performance. Isometric training is great for early stage rehab, but not for performance. The following is a link to an abstract that might help you with your position. http://link.springer.com/article/10.1007/s00421-005-0087-3
Isometric training can negatively impact an athletes stretch-shortening cycle (SSC). The SSC is important for all aspects of athletic performance.
If I were in your situation I would let the coach perform his isometric training, as long as it doesn't take away from the important dynamic movements. In my opinion barbell training is the way to go if you want to produce athletes. All you have to do is visit a top Div 1 weight room and you will see what all the top athletes are doing to get better. My bet is you wont see an olympic sprinter squatting against a wall for 10min to get faster.