This is true, as an engineer having to talk about this stuff, I used to put an emphasis on the dash as to not confuse colleagues and to clarify meaning that something was fully stored on the chain. That is because there was a time when we first had to work out the notion of what it meant to put something on a chain. That said, the losers of the onchain movement are NFT artists who truly built their artworks to render in the tokenURI function call of the ERC721, so that the artwork is forever stored and renderable. They‘ve even been trying to think of a new term like „in-chain“ to signify the differentiation between, for example, a Zora minter who „just“ puts the IPFS hash on-chain.
I feel like it's a losing battle and that truly onchain (pre "onchain summer") must use something like in-chain.