Asisreo
Patron Badass
Few problems with this example.It is the easy or medium difficulty encounter Conundrum. A 10th level party encounters a 18 pack of Ghouls. 12 of the Ghouls fail their saving throws to a PC cast Hypnotic Pattern spell.
The remaining 6 un-charmed ghouls fall quickly.
Meaningful combat is effectively over.
No matter how fast your group is, rolling dice is going to take longer then a Hand Wave; to arrive at essentially the same state and place.
1. Hypnotic Pattern isn't an every-enemy attack, it hits everyone in a 30ft cube. But why are they all within close to 30ft of each other? (The farthest is actually roughly 42ft). Are they all having a dance party? Was there an undead ball? It doesn't make much sense for them to be scrunched up before the party arrived unless there's a very particular reason.
2. The average amount of ghouls that would even be within this area is only 6, which means 10 of them are left over.
3. The hypnotized ghouls aren't dead, they can come back maybe up to a few turns later. As a 10th-level PC, you have a DC 17 which means in any given sample, you can expect 20% of effected ghouls to pass any given turn. Ghouls also paralyze over Con. It's an easy save but if a large number hits you, you might fail eventually which makes it worse since the hypnotized ghouls are now no longer hypnotized since you failed the save.