This is a woeful misunderstanding of how movies are made. The choice of actor can have a huge impact on the final product. Their performance, what they improvise, how the audience engages with that actor, whether it's with or against type and how that's received.

There's also the huge factor of how the presence of this actor or that one influences the budget. If you have a bankable leading lady or man starring in your movie Vs an unknown, the budget will often be millions more, which allows for better production value and a stronger supporting cast of seasoned character actors. Not always the case but the leads have a big influence on how well a movie does financially.

Yes the other departments matter as does the writing and directing. A great director can make a million dollars look like 5. That doesn't mean you have to totally devalue what actors do.