I’d be surprised if Proto doesn’t make a 1/2” drive extractor set.
Talking about dremel have you tried a burr or just a stone? You can go with a 1/8” or 1/4” shank die grinder. 1/4” with a burr will be faster but 1/8” may be easier to get in. I’ve used them to grind down hardened bolts plenty of times.
[This is probably some crappy brand and there are different styles but I use ball style burrs all the time for similar stuff.](SD-5 Tungsten Carbide Burr Rotary File Ball Shape Double Cut with 1/4''Shank for Die Grinder Drill Bit](https://www.amazon.com/dp/B0878S2KN4/ref=cm_sw_r_cp_api_glt_fabc_27P6MTDXRSCSCD9R7FEA?_encoding=UTF8&psc=1) just grind the entire nut and stud out until the wheel is loose. It’ll still take a minute but if you’re not able to find an extractor it’ll get it done. I seriously use a cheap pencil grinder from horror freight all the time at work (didn’t buy it myself) and it’s taken the heads off quite a few bolts.