85lc, my thoughts exactly!
If you look at everything, including the shooter, not just the cartridge with all aspects done as consistently as possible, then accuracy will naturally increase.
Look at the old .303, some rifles were far more accurate than others, even the likes of the p14's were tweaked to get the best out of them & they were good to start with!
The little 6.5x55, given its diet of normal 'military' ammunition which was of match quality back over 100 years ago was a deadly performer in the field.
True we understand internal ballistics a lot better than we did even 20 years ago, cartridges can now be designed around a certain powder & bullet with pressure & case size taken into consideration as well to be the most efficient size wise. Sure the latest & greatest are most probably more accurate than their predecessors, but this is due to better technology!
Are they more inherently accurate, that would be an impossible challenge as all cartridges are designed around different parameters, true some will be better than others in some fields like long range, but what we should be saying is that for the date that a certain cartridge is brought out, yes it is inherently accurate- for the technology of the time.
As to worrying about how good it is, in 10 years time there will be something even better yet than what we got now & the 'latest & greatest' guys will be flocking to it instead of the 6.5 Creedmoor which seems to be the flavour of the month!
I like what I like, my rifle & its cartridge does the job that it was built to do, it can still bring home the bacon so to speak, as to being the latest & greatest, sure it might have been generations long past, but frankly I don't give a hoot!
I get all my fun with reloading, just to see if you can 'tweak' it just that little bit better than what those other guys did when it was first out!