This is always such an interesting argument people make when nearly every 'next step' after undergrad is more selective than Ivy League schools.
Tier-1 Tech/Banking/Consulting/Law School/Med School all reject plenty of people from Harvard because they didn't do a good enough job there. Plenty of Harvard grads languish.
It's true that getting a degree is simple once you're in, but doing something with it still has capability-based gates.