I still kind of don't see how rsham is tier two. It has utility where priest has none. Priest does have great damage, but rsham has armor and mobility and can just run through attackers where a priest has to fight through them to survive (if you get out of position). I guess that's a situation that you would hope wouldn't happen in a premade, but in a pug it could easily happen. I think rsham has a better chance to re-position with it's 150% run speed. Also, it can fc in a pinch, where priest is like the slowest class ever, and can hardly keep up with a druid fc.
Don't get me wrong, I love my priest, but they don't stack well, and they lose a lot of their functionality if you've got 2 rshams on the other team, which like I said before, is a likely healing comp.
I feel like the 4 and 1/2 stars is accurate, but I worry that people will see priest in tier one and assume they are way better than restos, when it's really not the case. To me tier one is your best in slot specs for bgs, and you're going to want a rsham, if not two, in every comp.