Crypto to crypto transactions might be fast, but crypto to fiat speeds are still important. There's only a few exchanges that have true crypto to fiat pairings. If someone is day-trading they're going to want to have more than the 25000, at least in the US, to allow for day-trading and intraday trades, otherwise you get flagged. Three intraday trade flags and your account is dead for a while.
Coinbase is one of the few exchanges that has real access to real banking with denominated in real USD. USDT are not USD. I'm not saying Coinbase is perfect, far from it, but at least they haven't banned US customers because they're operating a USDT creation-scheme with it. As far as the insider trading goes, that's going to happen any and everywhere regarding exchanges that feel they will ultimately be able to evade prosecution on laws that didn't apply yet to cryptos, and especially ones that don't apply to the oftentimes hard to reach jurisdictions they've been set up in.
2018 will probably be the biggest real test crypto has as far as seeing if any mass adoption is real, which is why we need to keep educating people on real-world problems that can be solved with crypto, not just talking about the price action or how floods of new money will solve anything. If huge amounts of money really did solve anything, the world wouldn't be in the mess it is right now, considering how open those central bank floodgates have been.