You make some good points, but, my 10c - Not so long ago, if a calibre was in metric measurement, US shooters would not think it worthy, so overlooked the 6.5mm and it's ballistic advantages. How many 6.5mm Remington Magnums were sold? Now 'long range" shooting is a "thing", the 6.5mm in faster twist barrels ( and 7mm for that matter) have become popular. Without having to call them .264 or .284 so you could understand the diameter without reaching for a pocket calculator ( remember them?).
It's not so long ago that the .223 was only available in 12 twist barrels from the major manufacturers. Was it Tikka and soon after Savage that started offering 8 and 9 twist? Then we all wanted bigger 22's. to push the longer bullets.
The 308x1.5 was around long before it was domesticated and the 7mm BR Remington and 6mmBR Norma appeared. I have load data in an original "Pet Loads".
The ammo companies are more successful when reactive than proactive. Ammo made to satisfy a "need" will do better than one just testing the water. Many factory cartridges have failed, as there was no need for their existence, but those developed from wildcats in use for, say ,F-Class, PRS or Benchrest may succeed when becoming a factory cartridge- the Creedmoor's being the classic example, success when the parent 30TC went away ( we didn't need another 308). Others chase the AR15 market, looking for a better magazine length cartridge ( 6.5 Grendel etc). Anything the military use will always be the next big thing - 277 Fury, 30 Norma, 338 Norma.
The list of failures is long ( 10mmBREN, 244 Remington, etc) Things evolve. New cartridges arrive, others go. 6mm Remington, 303 British, 280 British, 7x57, 6.5 Swedish have all dropped in popularity, now bought by fanboys only ( me included, love my 303's) Some will make a comeback - .222, 6x45.
Just enjoy.