The 1v1 is easy as hell, except for the one high damage mob that is champion rank and is unkillable since he has double the hitpoints of his counterparts of same intended style of mob. I don't know if this is an intended design for 16 man normal but none the less we went ahead and killed him by having the other 15 of us finish our 1v1's and then come over and randomly landing shots on the mob every once and awhile.
we did that in 1st try
you just need to lead your raid better
what i mean is
a smart raid leader would know which player can handle that mob
if you don't have a player who can handle that mob than i suggest you should try 8 man