I don't want a union at OO.
However: My dad lost his medical for 18 months due to a congenital disease. The only steroid that worked for him was not FAA approved. With the help of a union doctor, he was able to get the steroid approved and is back to flying.
This is anecdotal, and a sample size of 1. And my dad is certainly not a big union guy, at all. But in my family's case, the help they provided was huge.