"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 ...