This is absolutely the right take. Major (A-list or superstar) actors are getting most of their pay from studio ownership, executive producer credits, residuals, licensing, or royalties. That ain't working class.
I'm fine considering small-time actors (and even many mid-level character actors without any real "leverage") working class, though. I think the replaceability criterion you mentioned is a good heuristic: if an actor could be fired and replaced without it changing the marketing, success, and appeal of the project, that's a sign they may be working class.