It seems to me that if they focus fire on the low AC nerds they could win easily
is that what they do? Or should I roll randomly on who they attack etc?
I introduced the rule that seemed good that I would announce who the monsters attack, and then the PCs could intercept and take some monsters on them.
That was good, faster than rolling a die for each attack (which, practically, ugh) and giving the players some agency.
But do the monsters then stay there for ever? Or can they leave? And then be re-intercepted by someone else?
One idea is that if they do leave without disengaging, the original interceptor/tank can "re-intercept" (keep) up to half of them, rounded down. (If they disengage they disengage. This is only if they just plain up leave.)
And then other protectors in the party need to step up to intercept the ones that get away.