It would be nice if the server owner could configure the use of the backpack upgrades or not. I can see why some people would like the feature, and can also see why some others woundn't. So if there is a toggle in a config to enable or disable the use of upgrades that would be neat.
Example:
New World - disabling the upgrades makes all backpacks the full tier when the player gets them
Existing world - disabling the upgrades makes all backpacks are upgraded to the max tier. Enabling the upgrades would keep all backpacks with items in them at the highest tier and all newly acquired backpacks will be tier 1 again. (as to not cause any issue.)

there's config option like that, the only difference is that the backpack tier is diamond not netherite

Oh nice! I ended up convincing the few people who were against it that it was an outstanding feature and we are all set now but that is nice that there is a config for that.