Furthermore, BIP351 only need notifications for the first interaction between two peers. After that, they can rely solely on SPV or Compact Block Filters in order to interact.

And they don't even need to rely on on-chain notifications since they can connect out-of-band via email, Nostr or any other communication medium.

In that sense, the featureset of 351 is strictly a superset of what SP offers and therefore superior.

Another downfall of SP is that it isn't even a standard. It's a stream of consciousness in a GitHub gist, without a real spec or reference implementation.