recovery from suppression is actually pretty quick if your squad is in cover. if units were still somewhat combat effective while suppressed, you would see more blobs than before. right now theres incentive to flank an mg team because of the harsh penalties of being suppressed.
in my experience it's often ~15 seconds, although it depends a lot on the situation.
i do not think they should be more combat effective though, i just think the mechanic would be more interesting if suppression was more fluid. you could suppress one squad that was getting close to your MG to slow it down and then concentrate on another one rather than suppress that squad and then change target, keeping both out of the fight or just getting naded, depending on what the game feels like at that moment. :/
that's a bit of a simplistic explanation, and kind of how it functions already, except that pinning doesn't happen unless you're retarded or drawing fire and suppression often doesn't prevent units from taking out MGs