This is quite misleading. -Locally-, it might be true that weaker students practice more than strong students, to compensate for their weakness. But on average, great piano players practice much more than mediocre piano players.
It's easy to find examples, but I'll name two that I found in my first two Google searches:
Lang Lang (virtuoso classical pianist) - 6 hours a day Oscar Peterson (virtuoso jazz pianists) - 6 hours a day
I'm --certain-- this is the norm, not the exception.