Well, you've been a Duran hater for a long, long time. Supposedly, Kelenic was the far superior prospect to you, but the Mariners dumped his ass this offseason because he has been a worse hitter than Duran so far.
MLB Network guys aren't the most reliable sources from what I've found. Maybe they just looked at his velo and said "oh, he doesn't throw mid 90's so he's less than and needs to go to the pen."
They are supposedly trying to cut payroll, but that would have been to sign someone, right? I think Castillo is the payroll you keep around and trim on the edges.
If you're the Mariners, you probably don't need an injured Mayer, but would be interested in Anthony and Teel. My guess is one of the big requirements would be a trading partner that has young pitching. Alas....