I've seen a ton of proposals similar to this and even thought of a few myself, and all of them fail to prevent a motivated and funded attacker from monopolizing

I've seen a ton of proposals similar to this and even thought of a few myself, and all of them fail to prevent a motivated and funded attacker from monopolizing a plurality or even 100% of mining. The only way around this is to explicitly identify miners (like Libra a.k.a. Facebucks), but that introduces centralizing forces. AFAIK proof of stake is the only approach that I've seen that could potentially work in principle but it has its own problems including encouraging wealth centralization, contributing to the deflationary nature of the currency, and being vulnerable to attacks by players with large fractions of the currency's float under their control. This is a hard problem. PoW works but at absolutely mind boggling cost.