I don't use Coinbase myself but here's a couple things that might clear your thoughts on the problems suggested above.

1. All exchanges have different buy and sell prices. This is the cut that they take, no matter what exchange you go to you'll see a big buy/ sell difference.

2. Fees are also a big part of all exchanges. It just means you should put that money in and leave it for a while so any fees are mitigated by large profits.

3. There is a huge influx of people signing up to Coinbase and its natural when everyone is sending money to them it'll take a while for it to be credited. They're trying to add more staff to deal with this every day. We can't expect them to add 100 new staff instantly, they do need to make a profit.

4. If you want to exchange between currencies then I'd suggest buy say ETH on Coinbase, then send it to another exchange that has ETH pairs e.g. Kucoin, Binance etc

5. As mentioned before they're a company of around 100 staff. It'll take time for them to grow with the demand they're facing. Support for all crypto exchanges are horrible at the moment. I waited a month to get a ticket cleared on Bittrex for example.

Hope this helped you. Not meaning to take stab or anything, these a genuine concerns most of the crypto-verse has atm.