I think that it is obvious that the pilots were properly trained. It is not often that the AAIB make concessions to try to understand why a pilot made a wrong decision, but if they felt for one moment that the pilots lacked proper training, then it would have been in the report.
It is a truism that most accidents are not caused by lack of airmanship, and this applies to this case. - imho.
I know in the cold light of day it seems an easy decision to make - what engine to shut down, but as you said yourself, the 404 is known for it's 'interesting' handling - therefore, the pilot had very little time and under extreme stress to make the right decision.
As I stated earlier, it's very interesting that all three surviving pax also heard the bang from the rhs of the a/c.
: DD :