The two aren't mutually exclusive. Canister powder used by reloaders has always been very consistent and max loads have gone down over the decades.

The 10mm cartridge is what prompted me to start reloading in the 80s. At the time AA7 was considered "the" powder for 10mm loads and Hornady listed a maximum of 13.9 grains for their 155 grain XTP bullet. I could not get there in either of the 10mm guns I had a the time. My Springfield Omega started showing pressure signs at a little over 12 grains. My 610 could go a bit higher but the primers started to really flatten out if I went over 12.6 or so. The last reloading book I saw listed 12.7 grains as the max which agrees with what I saw.

There probably are guns that could be loaded with the old max load and work fine. But mine couldn't. I think what happened if you go back 30+ years the reloading companies assumed you were really going to start low and work up to the best load for YOUR gun, like they emphasized in all their manuals. Not just load a bunch of ammo with the max charge and sue them if that blew up your particular gun. Now the max charge is more likely to be the lowest common denominator which is a shame.