I have to disagree with most of this. What I have found in this game is that it isn't so much the attachment, its finding the right combination of attachments and perks to see what works for you.
I have FMJ on several weapons,for example, and I find it to be very helpful in most situations.
I think that is the challenge in this game. You can't just slap a perk or attachment on a class and expect it to do work miracles, but if you find the right combination that works for you it is golden.
These are my experiences, at least. I experiment with different setups and find what works with my playstyle and class setup.