I agree: The military adoption of the .30-40, and later the .30-06, also coincided with the adoption of the box magazine, bolt action. This was " keeping up with the Joneses", because the European Powers had already adopted bolt action, box magazine rifles for their militaries beginning in the late 1880s. The Krag, adopted in 1896,and later the Springfield, adopted in 1906, were actually " Johnny-come-lately's" to the scene. Its main competition eventually evolved into being both the Enfield rifle used by the British, and the Mauser, adopted by Germany.
I doubt that anyone seriously believed that the .45-70 round was inferior to the .30-06. Using the Killing Power formula of bullet diameter, times, bullet weight, time velocity, divided by 100, the .30-06, 150 grain, 2700 fps round clocks in a KP of 1215. The .45-70, 500 grain, 1300 fps round clocks in a hefty 2925 KP! The real problem with the round was it was designed to use Black Powder, had a rim, and the balloon head casings of that period were not very strong. The military wanted to try a rimless casing, that was stronger, and used the Smokeless powders coming into vogue, to fire a smaller round for less felt recoil, but which would travel long distances in a fairly flat trajectory. The .30-06 beat the .45-70 on those fundamentals.
Having given the nod to the military choice of the .30-06, I have to say I strongly agree with Mr. Johnson. At closer ranges, the .45-70 is a terrific cartridge, and people regularly reload the casings( stronger webs today) to much higher velocities. With newer, bonded bullets, all that velocity delivers terrific energy on target at the short ranges involved. Yes, Marlin brought out the Guide Rifle, but the company was at least 20 years late.
Marlin 1895 rifles had been modified, ported, and loaded with " rhino rollers" way back in the 1980s by hunters. It was the guides who saw how well this old warhorse cartridge worked when properly loaded, who begain buying their client's guns, and ammo, and reloading dies, and retiring their .375 H&H Winchester Model 70 bolt action rifles. Try working the KP formula for a .45-70 loaded to 1900 fps. with a 300 grain bullet, for instance.( KP= 2565.) I have fired hotter loads, but this one will keep your attention, to be sure. These guns can still be loaded with Black Powder, BTW, for more modest velocities, and those heavy slugs will still kill Black Bear.
Since this forum is about Traditional MLers, and guns developed before 1865, or so, I digress, but not by much. The KP formula can be used as a measure of " Whompability" however, in either cartride or MLer guns. Mlers were being used by hunters well into the 20th century to kill big game, before the resurgence of interest in them in the 1950s. Today, plenty of bears, and moose, caribou, and elk are killed every year with BP MLERS. If you own a strong barreled percussion rifle, like the T/C Hawken, or Renegade, Or the Lyman Great Plains Rifle, they can easily handle 70 grains of powder, and more, and with some of the faster ROT rifled barrels, the will fire heavy conicals just as well as the Black Powder Cartridges of the mid 19th century did.