Why it's an issue: well because a broken and dead career seems to be the number one priority to me, it requires small changes and minimal risk in order to change the meta and allow more diversity in group play. Live developers did a shitty job on the mastery trees, I think we can be smarter than that here.
Solution : rework of the Loathing path
on the left current one, on the right what I propose

BG needs an aoe snare, he can't compete with chosen for too many reasons (neither BO atm). So his only chance is to get closer than BO and try to compete with him, BO gives huge DPS and perma aoe snare. If BG doesnt get an easier access to his aoe snare, it requires too many sacrifices for him to get it, gimping even more the career, we can say he doesnt have any aoe snare atm. If we bring aoe snare lower in the tree, BG will get the utility he needs without sacrificing too much. The aoe snare is totally balanced, since it has a huge CD (20sec) while BO is able to literaly spamm his aoe snare every 3 sec if he wants to. So BG should get his aoe snare at 10 points, the same way for IB, his mirror career.
About the swap anger => fop, most of the tanks have way to avoid dmg/punt and mitigate guard dmg except BG. BG needs one obviously and it has to be done without too many sacrifices (atm you need to invest 15 of your 29 points in order to get parry tactics and aoe snare, when most of the tank get avoidance/mitigation core or maximum 5 points investment in mastery (IB), it is not balanced atm. If Anger tactic becomes a 8 points mastery instead of 12, does it require to be rescaled? I dont think so, atm most of the tank can get avoidance/mitigation, SM, IB, Chosen, etc, they get 25%, SM is spamable, IB doesnt need any sacrifice either, chosen is interesting, because it's a 8 points mastery and tactic slot required aswel. But chosen get also a core ability 25% parry, at this point the unbalance is clearly obvious and leaving a 30% parry at 9 points mastery for BG doesnt sound too big at all, especially when we keep in mind that BG is rarely 100 hatred, so most of the time, you are around 70-90 hatred lets say, that means 21%-27% parry, sounds pretty reasonable to me.
In summary, my suggestion is to give aoe snare and avoidance/mitigation for BG in lane with others tanks, atm it's obvious BG is behind in both of those aspect, and he cannot compete and find a spot in grp, if we make those changes, it's not even about putting BG before other tank, just equal to most of them.
Thanks for reading