In general the Hollywood unions are very good for their members.

If there's a downside, it's that they used to act as a bit of a moat for the incumbent studios. Studios have entire departments devoted to processing issues raised by union members, which is of course expensive to do. And union members can only work on union productions, which meant tiny indie films could have problems getting talented people budget-wise. It's not just pay, it's meeting the requirements of the dictionary-sized "Basic Agreement" in terms of other aspects of production. That said, SAG has led the way to finding ways to accommodate smaller budgets and it's not as difficult as it once was.

It has a $3000 initiation fee that loads of people pay and never see the benefit of.

You will have to pay it just to do a short television appearance. It is certainly not worth that to everybody.

Then there are annual dues, whether or not you actually earned any money.

Then there's recent discussions of them kicking out long-standing members over their political views.

There might be a difference. Studios must first look for actors in the actors guild. That said, a studio has freedom not to use an actor. Similar, a studio does not need to use a bad script, and the studio does not need to pay a writer if it doesn't use the writer's work. In contrast, a factory has to pay for a worker, or even assign some work to the worker, no matter how bad this worker performs.