Well I think if you'd ask Dolphins fans the same question, they'd undoubtedly say yes. It's also been a big topic of conversation around here, both during the playoff run and the beginning of this season of how fortunate we had Tannehill as a cast-off of Miami sitting behind Mariota until it was clear that we couldn't continue that any longer. Sometimes the change of scenery works, but most often its a combination of coaching, available personnel and maturity.
As for the Henry question, the modern NFL is a passing league. So having Henry as a marquee player is a bit of a throwback. How many featured backs has Belicheck had during the 6 championships over the last two decades? A LOT. That being said, Henry is a special player and last year's rushing champion. What he brings to the table is a punishing battering ram style combined with an ability to escape for a long big play run at a speed he shouldn't be able to achieve. And he usually gets better as the game goes along, racking up more yards in the second half than the first. Defenses usually try to stack the box during predicted run plays and wrap up his legs in order to get him on the ground (or at least slow him down until help arrives). If you go high on him, you get the stiff arm and end up getting posterized like Josh Norman last week.
The other big advantage having Henry in the offense is that it makes play action far easier since the defense has to respect the possibility of Henry making a play when he's in the backfield. And Tannehill is highly effective on play action, especially to WR targets AJ Brown, Corey Davis, Adam Humphries and tight end Jonnu Smith. But frankly, any of the other role player guys are dangerous too in this situation.