Being interchangeable is literally why unions are formed. If you have some unique skill set that is valued, a union is unnecessary and would hold you back. If you’re happy being slotted in to whatever the next available position is based on your seniority with no regard to you as an individual, unions are great.
That’s why they’re mostly autoworkers or longshoremen and whatnot an not professionals, outside a few niches motivated by ideology.
Not necessarily - many games have custom engines underpinned by a decade of arcane tech that you wont find anywhere in the world outside the company.
It sucks both for you and the company if they have to replace you.
In contrast, if you work building SaaS apps on top of k8s, you can both transfer your skills easily, and the company can replace you easier.
It could go both ways, but in practice it usually turns out that if your skills are transferable you make more money.
This thing also popped up in the gaming industry, with Unreal becoming popular, and people using it making much more and jumping between projects, because their skills are transferable.
NFL players have unique skills, are highly valued, and are represented by a union. Same with most other major sports.