I was thinking, you don't really need blockchains for composability/interoperability, you just need open APIs

permissionless composability, blockchains do provide

but if there were theoretically some non-blockchain tech that just exposed open data, and the end-result product that takes advantage of this data is the same, then the blockchain part would not be necessary for the end product

there would also need to have some kind of open consensus layer so you know someone isn’t arbitrarily changing the data on the backend. Possible. Warpcast hubs are not onchain but have verifiable data.