First round quarterbacks have a 50/50 chance of success historically. Thus Tannehill has a 50/50 chance of succeeding. He will be our starting QB for at least three seasons. He and Philbin (and I suppose Ireland) are tied at the hip. This means that this debate will rage for at least 3 seasons.
The best the Dolphins can do is get him a solid Oline and some weapons (WR and TE) and see what he can do. Then he will either succeed or not. If yes, great. If not, rinse and repeat process.
I, for one, am glad they started Tannehill this season. I want to know what we have at QB ASAP. Moore was never the answer so what is the point of starting him? How does 9-7 or 8-8 with Moore help us long-term? He will be gone after this season. We should look to draft another QB or two in rounds 5-7 and UDFAs. That's what good teams do (see Pats, Packers, etc.).
Bottom Line: We will never be a consistent playoff team until we have a franchise QB.