Why couldn't you just sell tokens 1 for $1 and have their price pegged to USD? No PoW priming required. If stakers required rewards, you could just redeem 1 token for 99c and use the excess for rewards.
You aren’t actually wrong. Tether operates the way you describe: Based on proof of Trust Me Bro :P You can build derivative products backed by Tether. But, that’s a shaky foundation on which to build a new world financial system. You’d have to hope to spin up products that earn enough trust on their own to detach their valuation from Tether before Tether collapses.