One solid option wouldv'e been to install the wrench and give it a good percussive rap with a hammer to break the friction at the first sign of trouble.

Now with the head removed, a hit on the bolt with a punch to dislodge the friction/corrosion/bond on the upper thread surface of the bolt hole is the next best option. Then perhaps twisting the bolt by the threads from the backside if accessible.

Torx bits are a superior design against round-out. Always remember to try with the next larger size first to ensure you get the proper size wrench. And use sharp tools in good condition.

I secure rotors with torx bolts, copious amounts of blue loctite and torqued at 5nm. Which, because the Loctite sort of acts like a lube, comes very close to 7nm required of a dry installed bolt. If you torqued to 7nm dry, it stands to reason that even if you didn't over torque you may still have galvanic corrosion in the interface that lube or thread locker would have never let moisture in to initiate.

Good luck.

Also the "drill out the threads and use a nut/bolt combo in that hole," as suggested above is a reasonable permanent fix. All machinery designed for regular service over long service life has replaceable hardware as a matter of design. Bicycle hubs should be designed this way. If not for the shop labor component dealing with fiddly small hardware and risk of rotor contamination by service techs grubby hands, they probably would be.