As a cartridge and chamber designer/developer in addition to being a custom gun maker and competition shooter I can give some insight into the popularity of the creedmoor, be advised I'm a fan of the creedmoor but like Mtmuley and others have said it's nothing new. I first built a creedmoor about 10-12 years ago but it was around long before then as a benchrest round and later a highpower and F-class performer. The design of the cartridge is really along the lines of an Epps deign, think of P.O. Ackley but Epps preferred 30 degree shoulders over the typical Ackley 40 degree.
As far as the 260 argument, it's really a ford vs chevy argument between the two with benefits, albeit minor benefits to both. The 260 can gain slightly higher velocities, is it enough to make a difference, even in the competition world? My opinion is no, but shooters of the 260 in comp will say other wise. Quality brass availability for the 260, this is slightly going away as lapua is now making Creedmoor brass but the popularity is still causing some supply issues.
The creedmoor is more efficient per volume, hands down no argument to be had here. The design of the chamber (there's 100s of creedmoor and 260 chamber designs out there to choose from) promotes better precision, meaning it's easier to find a load that shoots and takes up machining errors and component quality typically better than a 260. This does mean a 260 wont shoot, plenty of them will but it's been my experience that 260 are bit more finicky on their loads. Keep in mind this is subjective, what I consider a mediocre load or group might be fintanstic in someone else's mind. If it's doesn't shoot well into the 0.2" or better for 5 shots at a 100 with good SD's then I'm not very happy with it.
Because it was intended for competition use, there were some parameters or rules in place that lead to the development, namely speed and caliber. You have to stay under 338 caliber and you have to stay under 3000 fps in most of these competitions, this fits the creedmoor great. When it was developed, it was developed to get the most use out of a standard short action length magazine. This is where it beat out the 260 initially, later on with better bullet designs the 260 came back strong. So much of the case with the then heavy for caliber 140s was used up in the 260 that it couldn't get the performance the users wanted. This again is where the 6.5x55 is lacking, it's an intermediate length case, meaning you really have to build it on a long action, at that point there's better options out there to do an even better job. Dont get me wrong, I love a 6.5x55 and with modern methods and pressures you keep up with and sometimes pass a 6.5x284 performance with a 6.5x55.
All of this said, I'm getting nearly 3000 fps (actual 2993 average with 2.3 SD) out of my creedmoor on a 25.75 inch barrel with the 143's shooting in the 0.1's with my chamber design and absolutely no pressure, in fact I'm about 8,000 psi under max pressure. I shot as fast as 3021 average but wasn't getting the SD's or the groupings I was wanting.
The timing and marketing behind the "release" of the creedmoor, the commercial release into the mainstream was truly the key to it's success. The 243 and even the 7mm08 (which is a favorite of mine and does amazing things at distance) got a reputation as a youths gun or as a womans gun so there was a stigma of not even considering them for quite some time. It seems that stigma is starting to go away.
Not sure if any of this helps anyone but it's something I have a lot of experience in not only in design and competition but in retail and custom building world.
