Either Matthews is an elite superstar that hasn't been used or Tannehill is a pretty good qb.
Between these two the nod definitely goes to Matthews. Matthews play significantly inflated Tannehill's numbers last year making his play look a lot better than it was.
Several plays Matthews made significantly boosted Tannehill's numbers...48 yard completion in which the ball bounced off the defenders hands and Matthews caught in stride, 46 yard TD catch in which a Hail Mary was severely underthrown and Matthews left the endzone going down to the ground at the 1 yard line and rolling in for a TD and an 8 yard slant he took 53 yards for a TD had little to do with QB play and a lot to do with exceptional WR play.
Overall Ryan Tannehill's numbers when throwing to Matthews:
43 of 61, 70.49% comp, 662 yards, 15.4 ypc, 10.85 ypa, 6.55 TD%, 1.63 int%, 121.07 QB rating (5th best ranking for a WR)
Ryan Tannehill when throwing to everyone not named Matthews:
320 of 525, 60.95% comp, 3,546 yards, 11.98 ypc, 6.75 ypa, 3.80 TD%, 2.09 int%, 84.98 QB rating
Literally throwing to Matthews elevated Tannehill's QB rating from 27th (84.9) to 21st (88.7) and YPA from 29th (6.75) to 21st (7.18) allowing for the first time in Tannehill's career to break the 7 ypa mark.
Football Outsiders has him ranked #2 in DVOA which is value, per play, over the average WR in the same game situations.
Miami averaged a meager 15ppg the last 5 after Matthews was injured.
That Miami's FO let Matthews walk for $5 mil per year after him being developed is beyond ridiculous and another example of decision-making leading to the Dolphins being a perennial .500 or below team.