As has been stated, The bullet length has more to do with stabilization than any other factor. 1 - 14" should handle up to 55 grain flat base conventional bullet. You have to try them to be sure. It should handle 50 grain bullets of any conventional design, including boat tails. I say conventional, because some of the newer style bullets of composite material or pure copper are longer than a lead-copper cup design.
As far as a 22 Mag or down loaded 223 covering a 22 Hornet - you are correct. A down loaded 30-06 will cover the same area that a 22 Magnum or 223 does + more on the top side. So why have a 223 or a 22 Magnum when a 30-06 will do it all from gophers up to Moose or Bear? You can talk yourself into most anything.
I have a couple of 22 Mags and a couple of 223's. I also have a 22 Hornet and a 22K Hornet, throw in a couple of 221 Fireballs. Why? because I want them, not because I need them or some thing else will due. If I were to have only 1 .224 caliber gun (including the 22 Magnum), it would be a .222 Remington with a twist rate of 1 - 14. It is easier to down load than a .223 and shoots almost as flat as a .223 and cases and rifle last a long, long time. The cost is cheaper that a 223 (less powder and cases can easily be made from 223's)
If I were to own only 1 center fire rifle to do it all from varmints up to the big stuff, it would be hard to beat a 30-06. If I were to lean to the bench crowd and only have 1 rifle, it would be hard to beat a 6mm PPC or 6 BR for longer ranges. I currently do not own either one, but I presently do have a 22 BR for my informal paper punching and long range varmint shooting.
Good Luck and Good Shooting
Good Luck and Good Shooting