I think you are pertaining on DEX built on Ethereum not in general. Fee on other like BSC, SOL and Polygon are extremely cheap.
Here's the thing, this new projects coming up this days calming to be decentralized aren't that decentralized as they calm. You think your transaction on Binance chain aren't been moderated. They're just centralized project riding on the downside (high fees) of the Ethereum blockchain. I don't know much about Solana but if I'm not mistaken the network was paused just few months back after it got attack while that of Binance, the network is been controlled by Binance itself.
I'm pretty sure, your coins can be easily frozen on this blockchain unlike that of Bitcoin blockchain. For low (fixed) fees you won't be getting total decentralization that's just how it works. All this blockchain having fixed fee price are just centralized and been controlled.
My biggest issue with the so called decentralized exchanges is that, they aren't totally decentralized, for example, Binance Dex has restrictions on certain regions and the hacks this exchange surfer are becoming alarming.