The current target is kinda the problem. It is trying to cram as much BG expenditure into 8 or 9 gcds as it can and this ends up making the burst very tight and ridged. Any lost gcds will lead to lost FCs. My suggestion is mostly focused on making it more flexible.
Squeezing in the Onslaughts (primarily intended as a utility action) is where your problem is coming from.Proposal to increase gauge generation instead of halving costs messes up that flow. Down to 10 gauge after FC+Inf+FC+Up+On, then you use preloaded Maim/Path for 60 gauge which leaves 20 after a FC, that's 5 GCDs out of 8. You need one of those next GCDs for Heavy Swing which generates no gauge, which means you can not use a 4th FC in the 8 GCD window (20+20 = 40, because the last GCD is for FC). The only way I can see to resolve that is have Heavy Swing generate 10 gauge so you can get the last FC and end at 0 gauge. I think it would be problematic to fit in the extra onslaught.
I believe the rotation in my suggestion would end up something like this:
Heavy Swing (Berserk + Inner Release) -> Fell Cleave (Infuriate) -> Fell Cleave -> Maim (Upheaval) -> Fell Cleave -> Storm's Path -> Heavy Swing -> Maim -> Fell Cleave -> Storm's Path end at 30 BG at 8 gcds and 50 BG at 9 gcds.
You only really need 4 gcds to get in the majority of the burst's potency which would make being interrupted during it less punishing.
The Fell Cleaves would only need to be about 800 potency and it would be much harder to lose them. In a 8 gcd burst you would be more likely to lose a 270 potency Storm's Path than an 800 potency Fell Cleave.Unless I'm missing something (probably) I don't really see that as a viable solution. Additionally, would you not have to significantly increase the damage from a single FC to make up for the fact you are replacing 2 or 3 500 potency attacks with 2 or 3 150-270 potency attacks? (ties back into the "Imagine losing an 800 potency Fell Cleave as compared to missing a 500 potency Fell Cleave.")