The assumption is that at some point Tannehill will be able to run an up tempo offense with more responsibility. There is no history to indicate this is so. In fact, coach Campbell last year said in the past Tannehill was given more responsibility and it affected his passing, so the responsibility was removed and played better.
Hopefully, Doughty will have developed enough at some point during this season to at least get a look. This offense has some legit talent on it, particularly if Tunsil solidifies the OL.