The Dolphins are really setting up Tua for success - the additions of Waddle and Fuller are significant. The line isn't great but he has a ton of weapons to work with. I do think his range of outcomes is perhaps the widest of any QB this year. I can see a scenario where he's a top 10 QB but I can also see one where he loses the job. I don't think the first scenario is hard to imagine - he harnesses Waddle, Parker, Fuller et al and they throw a lot. In the latter scenario, if he's playing poorly and turning the ball over but the team is still in contention, I can see them going to Brissett. Brissett is one of the better backups in the NFL (career TD/INT ratio of 31/13) and can effectively game manage. He won't win games for you on his own but he generally won't lose them, either. Don't get me wrong, I think Flores would be very unhappy if things panned out this way but if they are, let's say, 5-5 and Tua is playing as poorly as he did last year, I do wonder if they'd pull him, heading into Jets, Panthers, Giants, BYE and Jets.
Obviously, the most likely outcome by far is somewhere in between - he progresses, isn't amazing but is solid, and he keeps the job all year. He's someone I'm interested in because of the new weapons and the upside but I do think there's bigger downside than most other QB's, as well.