Sorry to say it, but he's doing preeeeeeeeeetty preeeeeeeetty bad.
You can check his overall performance here:
http://raidbots.com/epeenbot/eu/outland/yuuji/
Bear in mind most of his logs are ranked below the 50th percentile, which means 50% players on that fight did more damage than him... Considering he has close to BiS gear, and most of the people logged do not, that's pretty horrific. Don't accept gear excuses, 99% of the time it's total crap.
I'm not going to analyse logs for him. He needs to compare his WoL parses to other priests & see where he's going wrong. It's not just Warmaster he's doing bad, it's
all bosses.
- Check dot uptime
- Check buff uptime
- Check SW
on CD below 25%
- Check dot tick damage, and make sure you're refreshing dots at the start of procs (trinkets etc) and then again just before they run out
- Check reforges
- Check MS/MB rotation on SF, and check his MB damage compared to other priests to make sure he is using SF on CD.
He has a lot of work to do, there are ridiculously huge improvements he can make.