Both. Everything you said about the actor is true, and his work involves even more than that. I've worked with enough of them to know that. But there is more to being a musician than just reading music and playing an instrument.
At my limited level, I don't only have to play the notes in front of me. I have to play them at the same dynamic, same time and in the same style as every other sax player in my section, and often other sections. And we all have to play in the dynamic, time and style that the conductor wants - every time we play it. And then sometimes I get asked to go and sit in with another band. I'm lucky to get one run-through before the gig, when I have to fit in instantly with the rest of the band and how they're playing.
Pro musicians do all this and more, ten times over.
Both professions earn their money. The sad fact is that neither earns what they deserve, half the time.