Again, you're using starting data to translate to bullpen performance, which doesn't apply equally to all starters. Take some of the very best relievers in the league, like Dellin Betances, Liam Hendriks, and Brad Hand and predict their numbers as full-time starters. In fact we don't even have to make predictions since they were all bad starters which is how they became ace relievers in the first place.
Sanchez is a terrible SP and will most likely stay somewhere between terrible and bad. However, to the original premise, I would have an extremely difficult time non-tendering Sanchez based exclusively on his performance as a SP without even trying him out of the pen.