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

I can't find the cast, but I've said this for a while...open APIs have been around for a while, and I don't think touting permissionless is enough of a unique proposition to tout blockchain. 

Now if we say that it is an immutable single source of truth (but use layman terms), now we're talking.