Not vital, but definitely should try and get within a couple.. Keep in mind also that if a staggered enemy takes another staggered condition, they move to the 4th degree of failure.. Taking average toughness for PL 3 vs Average damage for PL 10, they should get knocked out pretty quick.. A toughness of 3 vs DC 25 means anything 11 (14 total) or less gets them staggered, two of those and he's out. They're knocked out by rolling a 6 (9 total) or less no matter.. Maybe your dice were rolling well for the toughness, which can happen and is sort of a flaw with MnM's system.
I seriously doubt the players were in any danger of taking any real damage in this encounter.. And they shouldn't be with that big of a PL gap.. However if they do not at least somewhat optimize their defenses, they can take damage and get staggered or worse by these guys, which shouldn't happen.. This should be a push over of a fight. Think if some player was only at say... Half cap for 10.. 5 parry 5 toughness.. These thugs that should be easy will hit him quite a bit (only needing a 12 to do so if they're average capped) and the hero needing a to beat a 18 to avoid harm on his toughness check to avoid damage.. The below average capped hero will probably win, but will most likely take some damage and is really only a few bad toughness saves from losing a fight that should, again, be a cakewalk.