The one thing that really doesn't sit right with me about the whole 'Marvel actors not knowing what movie they're in/what scene's they appear in' that I haven't really seen discussed on here before is that... it shouldn't be that big of a deal if a plot point is spoiled.
Like, movies shouldn't have to rely on the fact they have amazing twists and turns that the audience has never seen. Granted, some plot twists can be great and add to cinematic value, but if the shock value is worth not telling any of the actors what they're acting in then the chance is that the actual plot isn't executed correctly.
The best plot twists aren't completely a secret anyway. The best ones have foreshadowing or lead up to it in a way that you can't completely tell what's going to happen or do something so that while the plot twist itself is exciting, the fact that there is a plot twist is already known.
If plot twists are so important that Marvel would risk proper character development, actor rights and actual good acting, then the chances are that the so called 'plot twists' are actually just covering up the fact that the actual plot of the movie isn't impressive.