You can send different bloom filters to different peers too, so I'm not sure why you're listing subsetting as a unique advantage of prefix filters.

The main advantage of prefix filters seems to be faster lookups if the node is calculating a sorted index for each block, and the utxo commitment stuff, both of those would be cool but involve imposing extra costs on nodes. We lack models that let us understand the tradeoffs involved in various indexing schemes, I feel.