Yeah worst case Duffy can act as a bulk inning reliever at the beginning of the season and you would be able to stretch him out as a starter if someone goes down or if Kikuchi sucks. Kind of like how the Jays used Carlos Villanueva in 2011/2012 and Marco Estrada in 2015. I don't see him getting more than $5 million guaranteed. Depends really on his preferences if he wants to sign somewhere as a guaranteed SP. At least with Duffy, he can provide value out of the pen but I'm sure he'll get 10-15 starts over a full season.
I don't think many of the No. 5 starters left are worth bringing in at around $10 million when they aren't really upgrades over who the Jays already have.
As ST approaches, would look more at some MiLB possibilities. Forgot about Pineda, though he's a great example.