That's why startups exist, right? Startups start as small, focused, nimble entities moving faster than old established things. But, eventually the small, focused, nimble startup becomes successful and itself grows into an oversized sprawling entity.

YC isn't immune to becoming too big for themselves. It just opens up room for a new "startup yc" where everybody can have a strong initial impact again (until the new one grows too big too, then the cycle starts again).