Stealth is a great example. If you compare the rules involving stealth in Pathfinder 2e and D&D 5e, on the surface, it looks like 5e stealth is simpler to handle. PF2e has a chapter on it, 5e just tells you to roll stealth against passive perception. But the problem is that's not a complete ruleset, so the DM needs to fill in the gaps, and every DM is going to have their own version of the stealth rules cobbled together from dozens of ad hoc rulings which ultimately ends up being more complicated than if the rulebook just laid it all out to begin with.