How is that supposed to be the lack of Mastery ? Your shuffle uptime is 73% (which, on a tank swap fight where you have a lot of time to build shuffle for when you taunt back is REALLY low), you have windsong enchant and, the most horrifying, you only cast TWO freaking guards in 6 min. I know you're not supposed to have 12 in that time, but two... :-/
I'm not blaming you for not mastering perfectly your BrM (who, moreover is an alt if I undertand correcltly) and I remember myself having the same difficulties not so long ago, and actually I'm still not at the skill cap I wish I was. But this is not because you weren't full mastery, really.
Edit : By rereading that I feel that this might sound mean. I'm not trying to patronize or anything ; I should add that english is not my native language at all so tones are a bit hard for me.
If my post seems mean, I'm honnestly sorry !
However, I don't deny that for cutting edge players that do content for which they are undergeared, that's a logical choice. But not for 99.9% of the players, including those who have a decent HC progression ; therefore there's no point advising for that (in guides mostly).