People complain a short rest at one hour is too long. 4e had it at like 5 minutes.

People complain martials mostly just do their basic attack. 4e had every class have cool powers on the same recharge cadence. This also helped address the martial caster divide.

The other day I saw someone iteratively come up with "the attacker should always roll instead of confusingly sometimes the defender rolls. You could figure out like an AC for reflexes and fortitude and roll against that". Which is how I believe 4e worked.

It didn't have bounded accuracy, so changes to that tend to reinvent 4e, 3e, or Pathfinder.

That's off the top of my head. I'm sure there's more.