Guilmet has 5 strikeouts in 8 innings. Small sample size but that's not that bad. Combined with only 2 walks and 5 hits and he's doing quite well. I think you're reaching a bit for a reason to dismiss him. Estrada was an effective starting pitcher in Milwaukee until last year and West doesn't need to reach AAA to be called up. Plenty of people get called up directly from AA as you probably know. I think you're reaching for reasons to dismiss people here.
Well that's both simplistic and wrong. Let's say Bautista is out for 10 days. If you get 5 days of Bautista from not putting him on the DL than that's worth way more than 15 days of Ezequiel Carrera or whoever else you would have up.
If he was a lesser player it would be different but with someone as good as Bautista, the possibility of bringing him back before 15 days are up outweighs the value of the roster spot.