If they’re all shooting for the 95th percentile and have up-to-date data then you certainly won’t have fixing; rather you’ll get insanely rapid wage inflation!
It's possible the purpose of wage benchmarking companies is to allow bosses to say they pay the 95th percentile - which is useful to be able to say, when someone at an all-hands Q&A asks about raises and bonuses.
Then the benchmarking company simply has to define 'comparable roles' broadly enough to give the customer the result they want.