They were really counting on Seranthony, but also they got burned last year by having three well-paid to highly-paid relievers who couldn't pitch (four if you count Nicasio but at least he gave them something for a while).
One of whom they brought back but now he's cheap.
I think Suarez is the other key. If he can give you two decent innings a few times a week and Alvarez/Morgan can take the 7th or 8th, they just need one righty to step up, though two would be better. Maybe if Hunter stays healthy he has something resembling his past self, but he hasn't been able to stay healthy. Maybe it will click for Pivetta but also Velasquez could be in the pen pretty quickly. If he does well in the rotation you won't want to pull him, but would you want to see Eflin in the pen?
I guess you could also just make Howard a reliever this year if the starters are going well. He's on an innings limit and for the first month de facto tandem starts will also happen.
Definitely feels more "grass is always greener" than an upgrade, swapping Parker, Hughes and Morin for Guerra, McLain and Kelly. But they really drew that CBT line.