I believe it is a reference (not an absolute). At least it was for me! I shot fewer rounds through my 7mm RUM when I practiced. (Pullthe rifle out and see how 5 to 10 shots looked and put it up.) I could handle the recoil but not as well after 5 to 7 rounds.
With the 223, I will go through 20 rounds never getting to fire a shot as my 9 year old nephew wants to shoot too and eats the first 20 rounds before I get to play.theni dump the 50 round box down range between prone, kneeling (I stuck at this one), sitting and standing behind a tripod. When I want to humble myself, I shoot free hand. At the end of 70 rounds, I can still grab my suppressor bare handed (I am not rapid firing/mag dumping), I have little to no heat mirage a day I am not twitchy or tender.
I believe the above statement should be that 99% of people tend to practice exponentially more than people who shoot xx caliber bullets. This is due to lower cost/affordability and lower recoil / more enjoyable.
A bigger caliber does not make you a better shooter, more (consistent) practice does.