"Is FD slowly shifting focus away from ED?"
The short answer: No.
The long answer: No, we're not.
Devs leaving the project: People move around and change teams, this is called career development and growth and should be encouraged. We then bring someone in to replace them! This doesn't affect the development process because no single person informs the development of the game completely. I would say David has the most influence but instead of dictating the course and direction of the game he works alongside (in the literal sense of actually foregoing his own office to be sat with them and get involved in ideation and decision-making processes as a team) the designers, animators, programmers, audio teams, etc. I would say that it's actually the opposite feeling overall. Focus is higher on ED. We have ambitions, we have the beginnings of a roadmap, and the dev/design team are holding more meetings and planning sessions than I've seen previously in my two years here. This is something that the community have asked for and to do right by you we're putting extra time into the planning process.
So... no. We're not shifting focus away.
Let's hope the guys who thought about the Engineers as a mobile game casino level system are part of those who had 'careers developments'.