It will use third-party nodes instead of centralized servers. (Unlike trading on the exchange, I imagine setting up one of these nodes will probably require above-average computer skills.)
Using a third-party node sounds to me quite centralized and at the same time quite dependent on a third party that doesn't even know about its role in this.
The main problem with the current DEXes is absolutely 100% what you just said: they lack a good UI/UX. Look at something like UnstoppableSwap. Fantastic technology, but using it to do anything other than buy Monero with Bitcoin requires more technical know-how than 99% of Monero users have.
I completely agree with you on this. Desperate UI is the biggest reason why I rarely use the most popular DEX. Some improvements here would be very welcome.