Well we did something sort of similar to that last year. We brought in a former pro-bowl right tackle. Now, there is a big difference between the popularity contest pro-bowl and the elite all-pro, but the veteran lineman had an atrocious time adjusting until near the end of the season.
Mathis plays in a similar scheme and was a better player etc. But, OL is a lot about Synergy and chemistry. It takes time to build. Older players offer much less time post adjustment than younger players.
So, when you are building a team around a young QB, you want to put those cornerstone young OL in place to protect him for a decade.
What we should have done is draft Lane Johnson in 2013, but we didn't. We should have traded up to snag Lewan or Martin in 2014, but we didnt. We should have pursued the younger Monroe or Veldheer more vigorously. We should be on year 3 of building around Tannehill, but instead we are on year 1.5.