The first deer I saw shot was with a .22-250. It was still standing, with an exit hole the size of a basketball and daylight shining through. The guy who shot it was dressing out the larger doe. His son had put it down with a M1 carbine with AP rounds. This was about 1975. Both were not approved for deer in our state at the time.
You can use anything now - as long as it's centerfire. In the day, .22-250 was considered a varmint, and used on crows locally. Calling them in with recordings and pass shooting with a nice over/under was still to come.
I see the success of any wildcat as dependant on expected sales from public demand. It's like buying stocks on the market - you get some losers. Right now the .22-250 has been long acknowledged as the winner in the battle with the .220 Swift. Whether modern ballistics are better or not, the public thinks so.
Hence the popularity of the 6.8 SPC. It's got a history that sells, actually performs well even with the hype, and is getting offered by the major players. Like the .22-250, ammo is production line easy, and the number of available rifles to use it is huge.
Gunners argue the specifics of ballistics, but what makes the grade in the long run is public appreciation of performance with a solid reputation. The .22-250 has that - properly used, a given by responsible owners.
In MO, there are fewer farmers and more suburbanites, long distance shooting is minimal for many. So, the .22-250 is more a prairie dog rifle for a few. And the AR in 6.8 a much bigger opportunity - especially deer hunting, which is where a lot of interest is centered.
The game has to go down to sell the caliber.