Am I dumbing this down correctly?

Hey community. I got into a lengthy discussion with non-crypto colleagues yesterday who had good questions, and since I am no geek ( geek is a compliment in my vocabulary) .I tried to dumb things down to give a simple picture. Please school me if I am misrepresenting it: blockchain is like a blank computer ( made of lots and lots of computers) and Cardano, Ethereum, polkadot are the operating systems, like windows, iOS or Linux (no particular order) and Dapps are the programs that can run on various Operating systems, like Office, Adobe etc.. if I get this right, that means that users will choose their preferred system just like we do now, with trends following the type of usage, community and peer influence..and Dapps will have versions that run on all. ?