I think it probably does outperform the EF600 and 2X as that combo is f/8 which is a full stop slower.This lens is merely a curiosity, a museum piece. Like the EF 200 f/1.8 or the EF 50 f/1.0, there are superior alternatives to owning a lens merely for bragging rights.
No one will be buying this because it out performs an EF600 f/4.0 L IS III and a 2X III.
The EF50 f/1.0 is actually reasonably affordable and no other AF lens is that bright so it's still a great lens if you can afford it and works great with bodies like the R5 and R6 and 1DXiii or any eos body. Check out Ken Rockwell's review https://www.kenrockwell.com/canon/lenses/50mm-f1.htm