His argument is that DNSSEC is fundamentally broken, and you can't fix it via incremental improvements.

He is not arguing that DNS security cannot or should not be improved; in fact, he explicitly states the exact opposite.

I don't have an objection to doing a different DNS security system, and in fact I like DoH a lot. You can do DoH all the way back from authority servers if you like, and that addresses domain validation without boiling the ocean with 1990s cryptography the way DNSSEC tries to do.