Am I thinking about this wrong?
I wouldn't say you are thinking wrong so much, but you are not taking several things into consideration.
I’m a little frustrated with SAAMI and the way cartridges are frozen in time
Ammo specs have to be essentially "frozen" because guns are. Designs may evolve but after a gun leaves the factory it doesn't.
SAAMI is the Sporting Arms and Ammunition MANUFACTURERS....
It is made up of, for, and by the commercial firearms industry, and in my opinion its goal, after safety, is "what is best for the industry".
NO manufacturer is required to adhere to their standards, (there are some that do not) membership and adherence to SAAMI specs is 100% voluntary. SAAMI has NO enforcement power or authority
For example…270 WSMr2 …..running an 8 or 9 twist and with freebore cut for copper bullets seated to 3.0”OAL
There is nothing preventing a gunmaker from doing this, if they want to. You can get any barrel you want made, just open your wallet.
.or 6.5x55r2 loaded to 65000psi.
This, on the other hand is a different matter. Yes, in a rifle built for it, it could be safely done, BUT for the industry to offer a load with much higher pressure than the standard would be stupid, and they won't do it.
SAAMI ammo standards are set to be safe with every gun out there (in proper mechanical condition) that the round might be fired in. This includes all the older, weaker designs of everything that are still in use or exist and could be fired.
Old cartridge performances are "frozen" in time because there are old guns out there in use and new higher pressure loads for those rounds, while possible, are not safe in some older guns.
No amount of labels or warnings will prevent some careless person from putting dangerously high pressure ammo in their gun, if it physically fits. Along with this is the general belief and expectation that ammo made by a major manufacturer is, and will be safe.
Blow up a gun shooting "factory ammo" and the lawyers will line up to take the case. And remember, they don't need to win, to get paid.
The industry avoids this by keeping things within the long established safe limits, and not making rounds outside those limits that will fit in the older guns. One example is the .45-70 and the .450 Marlin.
The most common example of the idea is the .357 Magnum (and .44Mag) case lengths. They are made longer than the .38 Special, so the high pressure load won't fit in the weaker guns.
If some manufacturer does not follow SAAMI specs, the only thing SAAMI can do is say "this does not meet SAAMI specs". The "out of spec" maker doesn't get fined, punished, or even slapped with a rubber chicken.
The maker is on entirely solid ground when they say "we make this, it is safe when used under these conditions and may not be under others. If you use it under conditions outside what we specify, we are not responsible for the results."
You, or I, as individuals can ignore SAAMI standards if we choose to. And we are individually responsible for the results.
Just refrain from using them in the older M93 and M95 Mauser rifles.