> The correct formulation involves the subtle concept of decoherence.

The trouble is that decoherence only explains part of the story. With decoherence you end up with the probability density converging into multiple outcomes. But decoherence does not in any way explain that the choice is made to pick one of these outcomes.

As for what is wrong with QM, the main issue for me is the measurement process, which is just posited axiomatically. How measurement works should be explained by the theory but it is just posited. They assume a classical device that does the measurement. Decoherence explains bits of it but much is left hanging loose.