they're not the top dex anymore.
IDEX are not a DEX at all, let alone the "top" one.
For example, I read about dYdX DEX which is one of the famous Decentralized Exchange (DEX)
Because it isn't decentralized. They are a company with offices in California, and are subjected to all US laws and regulations. It is completely centralized - if the company goes under, then the exchange goes under. Even their landing page invites you to "Deposit $10 to get started." If there are no central wallets, then what are you depositing money to?
The majority of exchanges which call themselves decentralized are absolutely nothing of the sort, but the majority of users don't understand that, and so it works great as a marketing gimmick, all while offering no additional protection or security that comes with using a real DEX.
I would suggest if anyone has any further discussion regarding DEXs, either in general or specific ones, to open a new thread rather than bumping this one, since by doing so you are giving attention to OP's scam site.