Agree that burning ammo with smaller caliber is better. Always need more. But, practicing with the magnum thrown in for 10 to 20 rounds each range session after 100 rounds with smaller calibers can give you valuable feedback and gives a way to gauge improvement.
There are multiple skill levels involved. And recoil mastery is at the top of the skill list. Position, trigger pull, etc can be had with less. But, until you shoot the magnums you cannot improve.
If you shoot a magnum all the time, it’s hard to learn the finer points though.
A .22 will teach a lot, but you still have to shoot a .223 to master the added recoil. I think it’s the same way with a magnum.
You can shoot a million rounds with a .22 and half a million with the .223, but it still requires more for the magnum. That’s why I encourage having the magnum if you want to get there, because it gives feedback where you might be getting lazy with your form shooting a .223.
It’s like practicing 3 pointers hundreds of reps for form, but then shooting while defended for practice, then shooting defended while in a game.
Ultimately, you make a valuable point. Bullets down range matter and you cannot get better with out it.