.......Can it do anything a 6.5x55, a .260 Remington, a .257 Roberts, a .270, or a 7x57 cannot do?...............
MAYBE in the hands of one of the top two percent of long-range target-shooters, when competing with the rest of the top two percent of long-range target-shooters.
The little tweaks might even be genuine refinements, but I don't see any of them making enough difference for the vast majority of shooters to benefit from, particularly in production hunting rifles. That said, there are some production hunting rifles which will shoot like nobody's business, or at least better than most can benefit from when pairing skill and equipment.
The other guns are just not chambered to shoot the REALLY high SD bullets which make the 6.5 seem to have magical qualities - stuffed into a short action. I shake my head when short actions are touted for their lighter weight ans shorter length and then a 24" barrel is screwed on to squeeze out a couple feet per second to make it look like a shortened cartridge is as "good" as a longer, more voluminous one. The short action is reportedly stiffer and therefore supposedly more accurate too, but again, for the top two percent, maybe. Not me, certainly. Of course, pressure usually has to be boosted to aid in that aim as well.
Is it a "bad" cartridge? of course not. it does what a lot of other 6.5 (or other) caliber/case combinations have been capable of for ages. Take a 250 Savage, jack the pressure, use .257", 120 grain bullets AND have a tighter-twist barrel made and you have the same thing - with even better sectional density.
Oh, the bullets! Take any of the other cartridges and make sleeker bullets with better BCs and, voila!
I still prefer the older versions. The 6.5x55 works wonders in the "in-between" action-length of the old Mausers, runs at less pressure and are usually set up to shoot the longest bullets, as well as the shorter ones. The shorter ones (bullets) end up being in a range where there is a lot of competition among other calibers. The 160s, having been very common for the 6.5s for a long time were the real advantage for the caliber.
I'm not quibbling over tenths of thousandths of an inch on a 600 yard group among other shooters quibbling over tenths of thousandths of an inch on a 600 yard groups myself. I'm competing against squares of blaze-orange duct-tape at 50 or a hundred yards, pasted onto repurposed packaging material (cardboard sheets), so in reality, the CM offers me nothing and takes away a little (the longest bullets).
Would such a reality SELL the vast numbers of 6.5 CM rifles and boxes of boutique ammo that have been sold since its inception? Nope.