The union could flip hiring by making finding good candidates easy for a company by having their members pre-vetted, eliminating the need for vetting interviews completely. Hiring is a huge pain point and addressing it would, IMO, go a long way. And they wouldn't necessarily need to focus on employer negotiations as their members would find job hoping easy due to skipping all the vetting interviewing giving them leverage as individuals.
I feel like union would be much more symphathetic if they do this, and they can coexist with capitalism instead of being hostile activism. But this way they'll just be another corporation, with its pros and cons. Also programmers seems to be uncomfortable with the concept of formal vetting.