Like last year, the Cubs certainly aren't getting a lot of help from their farm system arms so far. Mateo, Stevens, Russell, Samardzija, and Coleman have all been awful.
I'm still a little bewildered why Mateo is having as much trouble as he has, though. He has some really really good stuff, and he has a 10.8 K/9 IP ratio. I think he must be going through a stretch of bad luck so far.