Obviously, as others have stated, the A, B and C system worked just fine. Why then does a "better" system (2.5 thru 5.0) create threads like this one?
IMO the reason is the (unrealistic) modern expectation that matches between members of the same USTA level will be decided by single break sets, ie that the matchplay will be even.
The USTA takes pains to explain that 6-0, 6-0 matches will take place between players that are correctly rated within their system, but still the erroneous expectation of close matches persists.
Welcome to the real world.