Tannehill isn’t bad, but their strengths are similar
Now, this article as a whole is painted to show why Marcus Mariota gives the Tennessee Titans a better chance to succeed than Ryan Tannehill, but that isn’t to say that Tannehill is a bad QB.
There are things that they (and I) like about Tannehill:
"Tannehill has various redeeming qualities, though. His overall accuracy rate (64.9%) was on par with Mariota (64.7%) in 2018, but when he misfired, it was clear as day. Both signal-callers performed admirably under pressure, too, with Tannehill generating a 73.5 passer rating (17th) and Mariota putting up a 76.4 rating (15th)."
Being able to handle pressure will be big for either QB while RG remains unsettled and with Taylor Lewan set to miss the first four games of the season.
If you are going to have a QB rated highly in any categories, accuracy and how they deal with pressure are both two boxes you would love to check.
So basically if you are looking at a best case scenario, everything that Ryan Tannehill gives you, Mariota can do better which really hurts any argument that you could make in favor of the former Miami QB.