I would call Bisq a decentralized platform. Sure, there is a centralized website which hosts information, user guides, etc., but the website is irrelevant to using the Bisq platform to trade with other users, just like you don't need to visit bitcoin.org at all in order to run a node. Other platforms such as LocalCryptos do make use of a centralized website to set up trades, but still trade in a decentralized and trustless manner.
It all comes down to the way you access trade liquidity. A litmus test for any platform would be like this: is it possible to deploy your own autonomous instance of the platform and still have access to the same pool of buyers and sellers? If the answer is affirmative, then the given platform can be characterized as "decentralized." If the answer is no, then you always have to rely on a central point of failure to communicate with counterparties, which is a clear indicator that such a system is far from being considered decentralized.
I'm not averse to using a centralized website if the trading itself remains peer-to-peer and does not require any trust in said website.
Doesn't any centralized website require trust that it doesn't collect and sell your data to third parties? Don't tell me you are ready to give up your privacy for convenience.
Interesting. I'll check this out. Do you use it? How big is the user base? What's the liquidity like?
No, I am not using it because it is still in early development, doesn't have GUI and currently doesn't allow swaps from XMR back to bitcoin. But if you are familiar with CLI and willing to exchange BTC->XMR, you can try this guide:
https://sethforprivacy.com/guides/bitcoin-monero-atomic-swaps/
