Earlier quoted context omitted.
I'm asking this as someone with 0 legal knowledge: doesn't the context matter? If every company takes this data and is like "we want to pay at the 95th percentile" (which is what they all do), that seems like wage fixing even if they're not all agreeing to it together.
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.