[I've posted this before but I guess I'll post it again since this topic has come back.]
After Heavensward, Creative Business Unit III pulled away some of the key developers of Final Fantasy XIV and gave some of them lesser roles coming into the Stormblood expansion. Some of the names I recall were Hiroshi Takai (Assistant Director), Mitsutoshi Gondai (Assistant Director), Kazutoyo Maehiro (Lead Scenario Writer), and Kazuya Takahashi (Concept Artist). The first three became 'Development Supervisors' for Final Fantasy XIV while Kazuya Takahashi is given the 'Special Thanks' treatment in credits. One of these guys, Hiroshi Takai, is confirmed to be the Director of Final Fantasy XVI so it does look like they pulled some of the top developers away from Final Fantasy XIV to work on Final Fantasy XVI.
On the bright side, this allowed some members of the Final Fantasy XIV dev team to step up and take on a leading role. If it wasn't for Final Fantasy XVI, chances are that Natsuko Ishikawa wouldn't be the lead Main Scenario Writer for Shadowbringers and its story would have turned out differently. Personally, I think Shadowbringers had the best story out of all expansions so I'm glad she stepped up. Also, while there will be overlapping developers since both games are developed by Creative Business Unit III, they are still separate teams within the same studio and Yoshi-P hired new guys like Ryota Suzuki to help with development of the new game.
My main gripe about FF16 though is that many of us FF14 fans play exclusively on the PC; so making FF16 a timed exclusive for the PlayStation 5 is a disservice to the PC players who have supported CBU3. Nonetheless, I'm still excited for the game. I just hope they don't keep us PC players waiting for too long because I'm already losing interest in FF7R (developed by CBU1 which is a separate studio from CBU3) which is still a PlayStation 4 exclusive.