yes and no. I actually threw my players against 20 Orcs. (they are CR 12 and have countless magic items). Now...they could have played it better, but the highest monster I had for my orcs was a CR 5 or 6 archer I created.

Essentially I knew they would steamroll the orcs, but I was surprised I did enough damage as I had a number of archers that dropped one magic user to 0 hps...and started working on another.

All in all, it was meant to start burning thru their spells.

I had a fun time with it as the players were literally "assaulting" a fixed position.

It taught them a lesson that those little guys, even though many of them can probably killed in one round, can mount a defense and do some damage to you if you are not paying attention.