IANAL but work in a technical field and have been an expert witness.
Had this matter been litigated on a level playing field, there would have been far more extensive discovery related to Exponent's work. Experts from both sides would have been deposed at great length, likely for several days. The testimony probably have taken a day or more for each side.
The NFL's process did not afford Brady/NFLPA a fair opportunity to explore the expert work in the level of detail needed to understand the accuracy/reliability of Exponent's work.
Commissioner Scheisskopf believed his expert and had no interest in even listening to any critique of Exponent's work. One of the difficulties techncial experts face is making their testimony understandable to the judge (or jury as the case may be). If the judge isn't interested, it's pretty easy to just try to make the issue seem confusing. That way, the criticisms don't really amount to anythiing, especially in the mind of a unprincipled simpleton like Scheisskopf. There's no way he undersatnds any of this because math is hard and science is boring.