Seems to me if the banks piled up a bunch of junk, didn't track who owned what, took advantage of the lack of bad information to make crap insurance look just good enough to fool the ratings agencies, and sold the resulting AAA-rated instruments for AAA prices, then the banks did a perfectly competent job making money for themselves.
The ratings agencies did a bad job, but that doesn't mean they weren't able to do better. They make more money doing a bad job so that's what they did.
The real incompetents were the investors, but the whole system was telling them they didn't need to be competent, that's what the ratings agencies were for.
The real incompetents are the developers of the system. It's clearly optimised to create the illusion of useful business activity out of bad-faith value manipulation and outright market fraud.
Of course they're not considered incompetent if they personally do well out of it. So perhaps the real problem is more systemic.
The behaviour of ratings agencies is very well depicted in 'Big Short', which essentially says that if one company won't do it, other will always agree to issue AAA rates.
The ratings agencies did a bad job, but that doesn't mean they weren't able to do better. They make more money doing a bad job so that's what they did.
The real incompetents were the investors, but the whole system was telling them they didn't need to be competent, that's what the ratings agencies were for.