The following is why your "Not entirely true," is not entirely true...
When understanding the schedule it doesn't just mean playing bad teams, it also means playing a team at home when temperature and injuries are a factor.
The Dolphins played at home with temperatures in the mid-80s and a humid day which northern teams generally wear down (see Chicago game this year) and Miami wore the Steelers down. This wasn't a game in which Tannehill carried the Dolphins to victory, this was a game in which Ajayi rushed for 204 yards and 2 TDs.
Also Roethlesberger got hurt in 2nd quarter.
1. Ben Roethlisberger was nowhere near 100 percent. Let's get this out of the way first. The Steelers are still one of the best football teams in the league, but operated with a roughly 50 percent effective Roethlisberger for the entire second half. Roethlisberger threw his first pick on the play he got injured on, then returned after the break to hurl a wobbling pass at a receiver with two defenders lurking clearly underneath. The team's final touchdown drive of the game was an opportunity for Pittsburgh to show just how deep they are at the wide receiver position, as Cobi Hamilton, Eli Rogers and Le'Veon Bell carried a one-legged quarterback to the end zone.
http://www.nfl.com/news/story/0ap30...-leads-dolphins-past-injured-big-ben-steelers
Other than beating the Steelers at home here are the following wins when Tannehill started that year:
Home Wins
1st worst team: 1-15 Browns by 6 in OT (Tannehill 3 turnovers)
2nd worst team: 2-14 SF 49ers by 7
6th worst team: 5-11 NYJ by 4
10th worst team: 7-9 Bills by 3 (Ajayi rushes for 214 yards and TD)
13th worst team: 7-8-1 Cards by 3 (Matt Moore led GWD after Tannehill done for season)
Visiting Wins
5th worst team: 4-12 Rams by 4
7th worst team: 5-11 chargers by 7
That was it under Tannehill...out of the 8 wins, 7 against losing records who combined for a 31-80-1 record (.279 winning %) by a combined 34 points including 6 in OT against the worst team in league, 7 against bottom 13 teams, 6 against bottom 10 teams, didn't beat a bottom 13 team by more than 7 points and the one quality win (Steelers) was at home on a warm and humid day with the QB playing injured during the second half.
As far as Maimi would have faired better in the playoffs with Tannehill, Matt Moore and the Dolphins offense literally out performed Ryan Tannehill and the Dolphins offense in every single significant category during that year.
Of course that is assuming Tannehill even gets Miami to the playoffs as the other times the Dolphins under Tannehill had a favorable schedule at the end of the season in the playoff hunt he choked each time.
Wins under Matt Moore:
Visiting Wins
6th worst team: 5-11 NYJ by 21
10th worst team: 7-9 Bills by 3
Overall out of Miami's 10 wins 8 of them were against bottom 10 teams, 9 against teams with losing record and the 1 quality is when Roethlesberger was injured for the second half on a warm, humid day at home.
You might think that is a playoff team. I call that a fortunate team the schedule allowing a team to play a lot of bad teams at home and that team played well enough to win close games.
To the Dolphins credit they consistently beat the bad teams, however that is not sustainable to getting to the playoffs on a regular basis which is why Miami only has been there one other time under similar conditions in 2008 since the 2001 season.