We have seen some head coaches hired in recent seasons and they haven't called plays on either side of the ball. I'm not sure why Bieniemy hasn't got a chance, but sooner or later he should get an opportunity.
A lot of Tampa's success might not have been down to Leftwich, however the same could be said about the likes of Zac Taylor and Matt LaFleur. Their opportunities because of McVay's success with the Rams. This off season Sirianni got a head coaching gig with the Eagles despite not calling plays with the Colts. Hires like that happen in today's NFL because lots of teams are looking for the next Sean McVay. Is Leftwich the next McVay? Who knows. It is fair to say he's worked with Brady last season and this season, but in 2019 he was their OC when Winston threw for 5109 yards and 33 TDs, though there was 30 INTs. So his experience is not all tied to Brady and he has been learning from Arians.