The notion that you must use all 7 modds for skills is not accurate, for example in my build i only use 6 abilities in pants, shirt and boots for i opted for armor instead, also some other slots I got a few weak abilities that if they were missing would not be bad. Crossbow could use some tweaking but I don't think it's in a bad state, it is mainly used for the % buff to epic attack and I've seen some very nice build utilizing it and making it work.