Obviously you weren't/aren't aware of how it came to be because you said it was "marketing". The cartridge was pushed for and requested by a certain segment of shooters and competitors that wanted exactly what it offers- something no other factory cartridge does.
If that segment of shooters/competitors was the only segment buying guns chambered for the cartridge, I would agree with you - but that most obviously isn't the case. Why?
If you don't ever shoot beyond MPBR, or can not comprehend inexpensive factory ammo with excellent terminal and external ballistics, low recoil and guns setup to shoot that ammo..... Then yes, I suppose it's "marketing".
Do you believe the mass market shoots beyond MPBR and comprehends the benefit of inexpensive factory ammo with excellent terminal and external ballistics? The majority of people who buy a gun in this cartridge can't (and hopefully won't try to) realize its full potential. Practically speaking, there is very little difference between the 6.5 CM and the .260 or a 7mm-08 out to 300 yards where the vast majority of game is shot.