The ordinals experiment has clearly shown that you can't stop non-transfer uses within the existing consensus rules.
We have been stopping them successfully before Taproot by making them non-standard which discourages such spam. Otherwise you could create a scriptpub with an arbitrary input that is a little smaller than 1 MB.
Pre-taproot, ordinal NFTs could also have used segwit for similar cost. Being non-standard might discourage them, but cannot stop them as long as they can be submitted directly to a mining pool willing to include them, as clearly happened.
And even pre-segwit, ordinals could have deployed at a 4x higher cost (without the witness discount).
So you're right about being able to discourage them, but wrong about being able to stop them.