Shield matters regardless of the number of monsters. it's kind of a myth that if you have more than 3 monsters the shield is irrelevant, of course the shield only blocks 2 creatures but more importantly it has both physical and elemental resistances (passive or imbu). Of course, if it's leveled high enough (above the standard level for crypt hunting) you can use 2-handed weapons, but the creatures hit so much that in my opinion, a few more attacks are not worth sacrificing the shield protection.