What server are you on? My own experiences (on Nightmare Lands/EU) are 95% good-to-excellent. Granted, I only PUG t1 FP HMs and I'm DPS, but, as far as I remember, I encountered only one quitter, and I do LFG HMs 2 times a day minimum after 1.3 hits, on both my lvl50 characters. Even if someone don't know tactics - he usually says so, and someone in the group always can explain it.
Same server. I was of the same opinion as you until recently, it seems that for every smooth run me and my friend get we get maybe one or two "derpy" runs. We sometimes run into much worse problems doing the daily normal for the 5 commendations, but we can carry a group through that even with bad DPS because there is no timer on boss fights. But when it happens in HM it just makes me facepalm.
I would like to add that I also attempt to add my own DPS during the low damage spikes, corrosive dart, orbital bombard, maybe even a shiv and backstab depending on the boss. I don't do this all the time, since my role is to heal but if the damage is low and everyone is topped up, why not right? But sometimes even with me doing that it still isn't enough, really does make me wonder how the damage can be so low at times.