they are faster and cheaper, but they are not kyc free, and a lot of people don't have access to CEXs for various reasons. so exchanges like eXch are their only option.
I would argue if those big centralized exchanges are always cheaper and faster.
There are many examples of people accounts getting frozen, coins confiscated, and they sometimes charge hefty withdrawal fees.
For eXch you don't have to register anywhere, no need to use email and personal information, no login, so for me eXch is faster.