Flybe don't run any MPL courses at EXT. They use 2 well-known FTOs to run the MPL courses which they part-sponsor. This sponsorship is repaid interest free over 5 years, so hardly a profitable enterprise.
As for the mass exodus, the seniority list suggests otherwise. As has been stated, it is a steady trickle of people, measured in single figures each month, and this creates only a small number of external opportunities currently filled by Flybe cadets on sponsored & mentored courses at 4 FTOs.
The number of internal jet opportunities has come about largely by the introduction of the E175 and the retirement of a number of older Q400 airframes on top of the 'normal' movement.