I agree that the 6.5 CM is a well designed round in which it’s design used the 6.5x55 and the 260 Rem for all the heavy lifting. But, "changed the shooting world forever," don’t know about that. If it was all that, nearly every shooter would have one, and that is far from the case. I fault no one for liking it and taking up the 6.5 CM banner, but it's really not that different than many others out there, the minutiae of advantages all add up to gain, but it's not breathtaking by any means. Let me put it this way, if we had a 6.5x55, 260 Rem and a 6.5 CM all at the firing line shooting to 1,000 yards it's not going to be the cartridge that makes the difference.
More than likely I will one day end up with a 6.5 rifle, no real desire at this point, but I'm pretty sure it won't be the 6.5 Creedmoor as it has already been eclipsed in performance by the 6.5 PRC. One can download 6.5 PRC to 6.5 Creedmoor loads, but there is a significant upside of being able to really stretch the performance versus 6.5 CM (to the tune of a ~200fps faster with 140's), this puts it close to a 280AI. So what does that say about whether marketing played a role or not in the rise of the 6.5 CM. The 6.5 PRC is what the 6.5 CM should have been some would say, like was said about the 6.5 CM towards the 6.5x55 and 260 Rem.
The reality is, is that the beat goes on and advancements are made, to take any thing away from the 6.5x55 and 260 Rem that blazed a trail isn't giving credit for storied service.
Now smokeless powder, non-corrosive primers, spire point bullets, scopes, better metallurgy, etc., these are what changed shooting sports forever in their own time and effect.