Dolphins aren't a great franchise, but they're not the Chargers. The Chargers are the unwanted stepchild of the NFL that literally doesn't have a single home game. Every single game they have might as well be on the road because their fans never outnumber the opponents'.
The Chargers also might have the worst luck, all things considered.
I don't think Tua's a top-10 QB. Probably more in the 11-15 range with Goff/Rodgers/Geno types. I would take (in no order) Mahomes, Lawrence, Allen, Burrows, maybe Hurts, Lamar (If you ever wanted to start a "who's overrated?" discussion, Lamar would be the second highest on my list, a distant second behind Justin Fields), Dak, Cousins, Brady, probably Stafford if he's not injured, before I would take Tua.
Tua's one of those guys that is fragile and seems to only be excellent when everything around him is excellent. I also think his success is much more related to having the best 1-2 WR punch in the league.