The physical resists of a Full Hiryu can get up to like 70% and is one of the few pets that can have MORE then GM wrestling on it. So with the right Hiryu, you could do much better then a Cu Sidhe as far as damage potential and resist. The factor I can't remember is what resists a Swoop have. I assume it is strong to physical as well.

Even though a Cu might not kill it as fast, a decently trained or better Cu Sidhe will heal all of its own damage so you can just point to kill and loot. And if you are really thinking, you can get a Cu Sidhe and a pack animal to carry all the massive loot!