You're not thinking probabilistically nor in terms of risk. There's no way to know for sure that an exchange is insolvent or at risk of becoming insolvent, but there are signs that increase the probability. Being run by amateurs is one such sign. Other signs are lack of insurance, persistent withdrawal issues, persistent arbitrage opportunities, lack of security reviews, poor technological practices (there are posts about the original Mt Gox codebase's poor handling of passwords for example, before Mark took it on), and misleading public statements.

If you bought the line that traditional banks were simply unable to process more than 10 wires a day, rather than it being that Mt Gox was so risky that they refused to process 10 wires a day, then you need to work on critical thinking. Likewise, exhortations that banks were placing restrictions on exchanges because "they were scared of Bitcoin" rather than being because these partners were shady and didn't have sufficient controls should have been met with suspicion.

And yes, Coinbase was also risky. The fact that things worked out doesn't mean it wasn't risky to begin with. I didn't give them any money for the first several years they were in business specifically because I saw them as high risk. In hindsight, Coinbase had the benefit of having backing by VCs with real business experience and subsequently hiring people with experience in the space, which reduced risk.