With an NFT you can prove the ownership of X digital asset, that proof of ownership is what is non-fungible
In order for NFTs-art to make sense to me, artist must attest that "whoever owns that digital asset in the ______ (ethereum blockchain?) " has the artist's recognition of ownership, and is a big UX problem for artists to really prove that, which I believe it's "solved" by platforms like opensea attesting on behalf of artist
So in practice, your buying the recognition of opensea that you own X asset, which opensea claims that is approved by X artist (it's also claimed by the artist on social networks or alike). there's still a problem there if the relationship between artist and opensea will be intact in the future, I don't know if or how they try to solve it
So in practice, most of it could have been done with a centralized database, but that would be missing the point.
There surely are knowledgeable NFT-creators who knows what they are doing and they can provide the attestation by themselfs, without any intermediary party, and that's where things get interesting with NFTs, look for example in gaming, especially where assets are shared among multiple games (otherwise it still could have been done with a database), it's just all impractical for non crypto-savvy folks