That's only really comparable if you're exchanging a few hundred dollars worth of crypto. What if you need to exchange several thousand? The spreads are going to be terrible, as would be counter-party risk. Timing would also be an issue, which is important if you're trying to trade (as opposed to HODLing).
The fees and inconvenience are only an issue for regular traders that are repeatedly buying and selling. For 6+ figure amounts it is even better to use 'over the counter' peer-to-peer services. Companies that are buying hundreds of millions worth are not using exchanges. I found it easy to do 5 figure trades even in 2014. There are significant fees and inconveniences when moving fiat to centralised exchanges so it evens out.
