Many exchanges = more competition = better exchanges
I'd prefer many choices rather than just a small number of exchanges handling majority of the cryptocurrency market. But yeah, hopefully we get more decentralized exchanges in the future.
It can be true but it's difficult now to find good exchanges between many of them.
I think that new users are confuse here and don't know which one to choose.
I personally using only 2 exchanges and it's more than enough for me.