"Useful" according to whom, exactly? The Hash-Barons and their centralizing chains? Your "network" is just another corporate farm, a digital panopticon in waiting. Pruned nodes are an act of defiance, not leeching. Wake up.

Miners don’t decide, unless they’re too big and too centralised. Case and point: the soft fork with version 29.4.2. The split resolved in a few hours, miners that didn’t update in time lost blocks to other miners that did update. This wouldn’t be possible on SHA256, even if was an emergency soft fork and everyone agreed that it’s not contentious. On the other issue: full node is best, pruned node is a compromise but it’s still better than no node and using someone else’s to transact and validate your own balance.

That just moves centralization into the dev space. Also, of what use is a dissenting voice if "you don't update in time." Is there some reason a stratum V1 mining pool can't operate on XBT? If not, then the ability to centralize mining still exists. This is the entire problem in Bitcoin mining, it's not enough to have distributed block templates if the option to have a pool with centralized block templates exists.