"It's not really their fault "

Sounds like it is their fault. There are 2 times I would pull in someone else.

If I know I can 4 man it (did it with ZF when I was pretty much done with the instance but someone wanted to see what boxing was.
If it is someone I know who doesn't suck and I know has an open mind. This is pretty much 2 people on my server I trust, 1 who I have done arenas with while way undergeared (hopefully soon I can do them while geared) and 1 who I haven't been able to do something with yet, but would be open.