Dr. Jin was at the FDA for enough time to see, their structure could allow employees to become entrenched and begin to erode untainted processes. Also more than long enough to see the futility of mabs to help the #1 CNS destroyer. He had a front row seat.
Somehow, he became aware of Anavex, possibly a professional interest prompted his decision to accept and offer to come on board. It's very unlikely he suspects any sort of funny business is going on, at any level, at Anavex.
The long wait between PDD P-2 and possibly P-3, just makes sense. Waiting for the PD to be funded, gathering data and focusing upstream was the obvious choice. It's accepted, getting working neurons to recover is easier than non working, which is when the PD patients suffer from dementia.