The buffs are nice for those who prefer to play Slayer. Thane is still stronger on AoE where Slayer is stronger single target.
That’s a fine place for things to be for the spec, but overall Fury still needs help in M+. It’s not like it getting bumped a few percent in raid would hurt anything either.
That said, I agree with you. It should be fairly simple. You focus on Thunderblast and Odyn’s Fury (since they just buffed Bladestorm).
Odyn’s Fury would further help Slayer find a place in M+, but it legit needs to be buffed by 75-100% to be worthwhile. Even with that kind of buff it’s unlikely Thane would want it - it just doesn’t fit as well into the Thane toolkit and priorities.
Thunderblast - buffing this for Thane is powerful as a consistent soft capped damage source. It plays into the sustained nature of mountain thane and would help Thane keeps its identity in m+ against Slayer burst (if they actually buff OF)