Exchanges are needed to not give the monopole to only a few exchanges. But how many do exchanges do we need? I don't really know.
If thoses exchanges are not needed, they are going to disappear by themselves. Time will tell us which exchanges are going to survive or not.
I think we need a maximum of 4-5 exchanges in the future. now all exchanges are being finalized with technology and therefore it cannot be said which exchange will be unique