Reddit mentions of Diablo DS0608CF 6" Carbide Tipped Reciprocating Saw Blade

I believe those nuts are crimped, and the threads are probably rusted and fused solid. You're in for a fight.

I got a Milwaukee 2767-20 M18 1/2-Inch Impact Wrench with Friction Ring specifically for dealing with problems like this. It is amazing and has saved tons of time. But an impact wrench might not work if the torx head is damaged enough.

Skip the torch. If you can't get an impact on it, your best bet is to cut the bolt off. You have three options: Cut the nut-side off and punch the bolt out through the bushing and axle mount. This won't work if the bolt has rusted solid to the steel insert in the bushing (it probably has). Option two is cut through the bushing directly next to the mount, and punch the bolt-head out. The last option is to cut the torx head flush with the mount and punch the bolt out along with the bushing.

For cutting, I recommend a saws-all with a carbide-tipped blade as the safest option. Be careful to not cut into the mount too much. If you don't have a saws-all, you could try to cowboy it with an angle grinder with cut-off wheel. Check clearance and geometry to make sure the wheel is actually big enough to cut through before the grinder shaft or body hits. If you cut the head, hit it with a flap disc on an angle grinder (most under-rated angle grinder tool IMO) to get it flush with the mount so you can punch it through. Hell, you could flap-disc off the entire head - would probably be safer than using a cutting wheel under there. 40 grit flap discs take material off amazingly fast.

Apologies for the long post. I've been where you are and like to help folks who are trying to help themselves!