Isn’t most of his accomplishments due to being strong-armed by BE and CDU in confidence-and-supply agreements?
I’d really appreciate it if my question is answered by someone knowledgeable about Portuguese politics.
No, on the contrary. BE and CDU didn't gain anything from supporting the PS in 2015. The CDU achieved their worst result in history, while BE dropped from 10.2% in 2015 to 9.5% in 2019. In fact, Costa's main accomplishments are the economic growth, the balance budget and the fall of unemployment. In terms of labour laws, with huge impact in the employment figures, Costa forged a deal with PSD, leaving BE and CDU out of the deal. BE and CDU were able to force some of their flag policies like pensions increase, and some wage increases for public employees, but, overall, you can say the for almost 4 years Costa had BE and CDU in his hand, and didn't fear them.
About Costa, I would say he's leaning FF. He's not the worst PM ever, but also not the best. However in this crisis he has been very good in controlling the situation and trying to make everyone feel calm and safe. Now, the next economic crisis will an even bigger challenge for him and for us all.