Besides Rondon and Bassitt, I don't think there are starters out there that warrant a rotation spot ahead of what's already on the roster.
Manaea was the ONE guy I could see adding to that mix, but he's old enough now that I think the chance of hitting his upside is about worn off; the most likely outcome is that he's a back of the rotation arm.
Plus, with Walker and Taillon getting obscene contracts, this kind of smells like Manaea may have preferred to go back to the Bay Area instead of taking a better contract elsewhere.