I looked into this more and the IRS apparently sets an "Employee compensation limit for calculating contributions", which is currently $290k. So 4% of your salary on a match ends up being $11.6k, which is slightly better for highly compensated employees than the max $9.75k for a 50% match, but of course is significantly worse for people making way under $290k (i.e. most people).
Also worth pointing out that the all-source IRS 401k contribution limit is currently $59k/yr, so even with an insane 500% no limit match or something that manages to pass the safe harbor test, there still is a limit you'll hit eventually. It's high though.
Ah, yes, you're right: I forgot about the contribution limit. Technically QNEC/QMAC can still be used to increase beyond that, because they're not computed off of compensation--but that wasn't your point.
Also worth pointing out that the all-source IRS 401k contribution limit is currently $59k/yr, so even with an insane 500% no limit match or something that manages to pass the safe harbor test, there still is a limit you'll hit eventually. It's high though.