All you need is the utxo set to know if a tx you recieved is valid. Meanwhile the node syncs the chain in the background to eventually validate that the assumed utxo set is indeed the correct one. See https://blog.lopp.net/bitcoin-node-sync-with-utxo-snapshots/

This is the exact usecase for assumeutxo. You can use it in Bitcoin Core v29 but it's not the most user friendly experience.

How are they not money transmitters already?

The reason the minRelayFee filter works is because there is very little economic incentive to bypass it. It is cheaper to just bump your fee to 1 sat/vbyte. This is not so for larger OP_RETURN txs or other types of non-standard txs.

Coyotes do this with the rabbit in their jaws.

Wow I have never seen her be so polite to anyone.