The risk in 1 & 2 is that monsters become a slog and characters are no longer heroes. If you need to hit a monster 30 times before it dies (because half misses due to AC, and you need a lot of hits due to HP), it’s just slow and boring.

Lair actions and distractions/barricades to get to BBEG are where its at. There’s a trap in the way. New support keeps popping in until something is destroyed. Something changes drastically halfway through the fight.