Yeah, I think talking about the benefits of "unions" in the abstract is a little weird because - at least in the US - unions are highly regulated by laws that were written primarily envisioning the model of early-20th-century manual labor. That is to say, unions were designed in a way that fit not just for-profit businesses but very particular types of for-profit businesses.
So you need to separate the more conceptual parts of unions - that maybe we should value sustainable and secure employment over shareholder value, that laborers should be able to negotiate collectively and not individually, that you can do good work that is beneficial to the public by prioritizing happy laborers - from the very specific implementation of unions that we happen to have. Without our current model of for-profit businesses, the implementation of unions would not be a coherent concept (and admittedly they are a bit less coherent now and when applied to e.g. tech companies than they were in the past for the businesses for which they were designed - which isn't to say they're the wrong answer, just that they're an awkward fit). But the values are still valid.
As a sibling comment said, worker-owned cooperatives are one model here. Another similar option is very small companies: the concept of a solo founder unionizing makes no sense, but the solo founder of a bootstrapped "lifestyle business" has most of the benefits one generally wants from unions, and communities of such businesses can choose to federate for a better voice in the market. There are certainly a lot of other options besides the idea of a large business owned by its founders or publicly traded.
But really developers would be better off with something along the lines of a trade guild. Something that enforces standards on employers and employees.
The Saturn corporation had a labor-management partnership which did exactly that for standards, and was a subdivision of GM. Unfortunately it's stressful for corp and union leadership when high standards are set, so it eventually lost support despite high worker approval.
So you need to separate the more conceptual parts of unions - that maybe we should value sustainable and secure employment over shareholder value, that laborers should be able to negotiate collectively and not individually, that you can do good work that is beneficial to the public by prioritizing happy laborers - from the very specific implementation of unions that we happen to have. Without our current model of for-profit businesses, the implementation of unions would not be a coherent concept (and admittedly they are a bit less coherent now and when applied to e.g. tech companies than they were in the past for the businesses for which they were designed - which isn't to say they're the wrong answer, just that they're an awkward fit). But the values are still valid.
As a sibling comment said, worker-owned cooperatives are one model here. Another similar option is very small companies: the concept of a solo founder unionizing makes no sense, but the solo founder of a bootstrapped "lifestyle business" has most of the benefits one generally wants from unions, and communities of such businesses can choose to federate for a better voice in the market. There are certainly a lot of other options besides the idea of a large business owned by its founders or publicly traded.