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. I couldn't think of a downside as of now. But yeah, hopefully we get more decentralized exchanges in the future.
Yes, having the same type of businesses within one ecosystem is that they create a stiff competition for themselves and that certainly will benefit the consumers. In this case, knowing the number of exchanges popping up every day, no exchange will certainly not want to stay non relevant in the long run and will try as much as possible to do what they can to stand out among other exchanges, which means there will be no room for slackers.
Yeah, exchanges and many of them is not a bad thing for the community. Obviously, some will try to stay relevant by upping their game; some will definitely not and then at the end of it all, end up not being able to cope with being in the market. As long as stiff competition is being created, which is what huge number of exchanges will create; it would make investors happier to use any trusted platform to carry out their exchange without any issue.