Should be 3 game lead, not 3.5. Dolphins are 2.5 games behind us, we have the tie-breaker, so even another 0.5 gain gets them the division lead.
That being said, Tua's return could boost the 'phins, assuming he stays healthy, which is a big if. The Jets are a bewildering dumpster fire at this point. The Pats are, well, terrible. It helps as in, if the Bills don't screw this up (like the 'phins last season), they should be an almost lock to make the playoffs and host at least their first playoff game at bare minimum. So, it certainly helps.