I'm a PhD student in English and you'd be hard-pressed to find any professor, other than ancient ones on the verge of retirement, who buy into "older authors are better." Even my undergrad Shakespeare professor recognized that Shakespeare wasn't inherently "better" than contemporary authors, or even playwrights of his time.

And you would never find a scholar of drama who thinks reading a play is just as good as watching it but there are a lot of financial and logistical reasons that it's difficult to teach a lit class and watch those plays. Even film versions will edit parts out. For example, the frame-play of "Taming of the Shrew" is almost always cut out of performances, on stage or screen, but it's an important part of understanding the "know your role" message of the play.

That said, my Shakespeare professor assigned all of us to groups and each week one of the groups would have to perform a scene from the play we read that week twice, leaving the lines the same but changing casting, blocking, costumes, etc. To see how the play was more than just the text.

Also, plays not being performed or epic poems not being sung doesn't really answer why the canon is being taught so much. It isn't just English departments dictating what is "good" literature, there's also a lot of pressure from outside the department. Not even my Shakespeare professor thought a Shakespeare class should be required for majors, but the administration thought "of course it should be because Shakespeare is the best!" Also, those classes tended to make more often because students were more interested in a class on Shakespeare than, say, a class on afro-futurism.