I definitely don’t believe that to be the case. Each mechanism has its issues and both will eventually require aftermarket parts, especially with heavy use.
The things I see problems with on Stern mechs are EOS switches that break, EOS switch pawls that break and coil stops that break but the latter has generally been better using parts from Pinball Life. Of course that could be dumb luck too, no idea really.
The things I see problems with on WPC style mechs are cranks that wear out very quickly (either the hole for the link gets super sloppy or the crank down hardware collapses on the bat shaft very easily—both of these problems seem related to metal that is too soft) and entire brackets that crack or shear at the coil stop end.
Wear and tear for things like plungers and stops, under normal circumstances, are normal between the two mech designs as best I can tell. I’d generally prefer to repair or replace the Stern parts for the above issues vs. WPC parts which are a bit more work to get apart and change. Cost is close enough that I don’t really care. I like the feel of WPC flippers better but that’s not down to solely the mechanism as Stern flippers function differently than WPC.