It’s not supposed to stop all spam. To do that is impossible. It’s a message to VCs that despite what Core signaled with v30, spam is not welcome, and will be mitigated, so stop funding spammers. As you point out, it’s only a minor disruption for ordinals, but it also closes the very simple ...

It stops Ordinals in its current form and destroys their shelling point. The will have to rebuild everything from scratch. And when Knots is the dominant client after BIP110, our *working* new filters will take care of their new scheme a lot faster than any consensus change.