When you think about it, OpenSea would actually be much "better" in the immediate sense if all the web3 parts were gone. It would be faster, cheaper for everyone, and easier to use. For example, to accept a bid on my NFT, I would have had to pay over $80-$150+ just in ethereum transaction fees. That puts an artificial floor on all bids, since otherwise you'd lose money by accepting a bid for less than the gas fees. Payment fees by credit card, which typically feel extortionary, look cheap compared to that. OpenSea could even publish a simple transparency log if people wanted a public record of transactions, offers, bids, etc to verify their accounting.
However, if they had built a platform to buy and sell images that wasn't nominally based on crypto, I don't think it would have taken off. Not because it isn't distributed, because as we've seen so much of what's required to make it work is already not distributed. I don't think it would have taken off because this is a gold rush. People have made money through cryptocurrency speculation, those people are interested in spending that cryptocurrency in ways that support their investment while offering additional returns, and so that defines the setting for the market of transfer of wealth.