The 6mm Creedmore is not identical to the 6XC. It is (in my opinion) a very specialized niche cartridge.
The .260 Remington is very popular with NRA High Power target shooters because the long bullets buck the wind and get sufficient velocity so they are very accurate. The Creedmore round has one or two tiny advantages, mostly regarding long bullets fed from the magazine if I recall correctly. I didn't think they were important.
I think the real purpose of the Creedmore round is to transfer money from target shooters to the Creedmore company. For hunting,it has no purpose that a .243 cannot do better. Barrel life is better but hunters usually don't shoot enough to notice the difference.
