His first response there is all you need to read - the purpose of the mempool is to model what’s going to be mined. If you understand that, it has great relevance to your proposal; for example, when you say
… surprisingly it’s the opposite that’s true: decentralization is improved by not pushing policy to node operators; if nodes are in sync on the candidates for mining, propagation and block reconstruction is faster (and fee estimation is better, side effect), which makes Bitcoin’s decentralization better. Mining would be more centralized if everyone was blocks-only, and that’s still true if everyone’s using different policies for what they see as candidates for mining.
(Not that I’m saying you shouldn’t have control over your node’s policy, of course, you do - I’m saying that it isn’t helping the network; it might help you in some way or other, e.g. if your node has specific constraints on resources perhaps)