Yeah, I kind of agree, the only reason I can see to add a starter like that right now would be to hedge against injuries I guess.
Part of me wants them to add a Montas/Castillo type SP, but another part of me would rather they hold onto their bullets so they can make a legit play for a true difference maker should one suddenly become available, like Shohei Ohtani for example. Of course, that's the pie in the sky, unicorn type pipe dream, but if an actual ace SP were to hit the market you'd hate for the Jays to have already blown their wad by adding another Berrios. Guys like Montas and Castillo will be free agents in a year and a half. Wait and try to sign them if you want them down the road, but for now I'm kind of OK rolling with Manoah/Gausman/Berrios plus whichever other starters they have to round out the rotation. Stripling has been solid, Kikuchi might figure it out and be more consistent in a good way, maybe Tiedemann pulls a "Manoah" and is in the Jays rotation by June next year. Or maybe Frasso does.