I think Valve sets a good example for an alternative, while not union they operate with a flat structure and is not publicly traded which sets them apart. They're kinda like an elite guild of game developers.
I'm not really sure how you could know this? For all we know all the employees are unionized and haven't felt like they need to push management for official recognition.
If a union had managed to organize the most profitable-per-employee company in the video game industry, it would have been front-page news.
That's my point. There is no requirement in the US that you organize explicitly. You could just as easy do it without requesting recognition.
Valve doesn’t release that many games though.
Presumably they subsidise the good conditions, few but high quality releases etc with the Steam store, which does set them apart from most studios.