IOTA and NANO do not use blockchain. I think in the medium term, it is impossible to come up with better and safer technology. I think the debate will only take place in relation to the nodes because maybe they change, the POW PoS debate and some other issues.
But Blockchain is here to stay. Just like the internet.
My understanding is that NANO uses blockchains, with a separate blockchain for each account (I'm not familiar with the technical details so I'm not sure how to define that.) It seems to work very well at any rate. It's like Bitcoin+Lightning Network except free (not merely cheap), and without opening/closing TX on the blockchains or the other complexity of LN.