If most Hollywood movies featured mostly ordinary looking actors but with excellent acting, then I would've agreed with you that the acting ability is valued more.

There are a few genius actors that made their way into Hollywood because of acting, not looks. But they are an exception to the rule. The vast majority of movies are mediocre and feature rather attractive actors (actresses in particular) whose acting is very basic and non-remarkable.

The fact is, there are way more attractive people than there are talented actors. So it's easy for Hollywood to make being attractive a prerequisite, and still get good actors