I thought one of the advantages of the bounded accuracy approach was that you could use (say) 12 CR 3 monsters to challenge a high level party. A band of CR 3 monsters doesn't need a world-shaking agenda (although they will presumably be doing more than stealing cows).
I've no idea if it works in practice, since I don't play 5e, but it seems to work for S'mon.
Yeah it works fine - I'm not using any CR 20 creatures vs my level 14 Primeval Thule PCs. 12 CR 3 plant zombies with AC 13, 52 hp, +5 to hit & 3 attacks (grappling vines & 2 slam) for 8 damage/hit worked fine on Wednesday.