RPGMemes

1, 2, and 3 are easy options, but lazy AF and deeply unsatisfying in most cases.

4 and 5 is really where it's at, but it's quite a bit more work. 4e's early maths was really bad, with enemies becoming enormous damage sponges, though they were otherwise probably better than 5e. Late 4e improved its monster design somewhat. Pathfinder 2e is great, so borrowing monsters from that could be good. Or Matt Colville's books for 5e.