The only game type where I find grenade spamming to be a problem is any CTF (including Stockpile) game. It's almost impossible to recover the flag because you have to sit there, vulnerable, for 10-15 seconds. All the enemy has to do is lob a grenade and give you a whack to the face and they've got your flag again. Possible remedy is allowing the flag recovery to go faster the more team mates you have around it.