I think that, if you are a subscriber at a theatre that presents largely new work, part of the deal is that you acknowledge that not every production is going to be great or even good. But I would think that the reason you're subscribing is that you like the game of chance or that you have a reasonable expectation that you'll see something over the season that makes all the not-so-great stuff worth it.
So there's never going to be a guarantee of anything, including the titles presented in any given season. That's just part of the bargain. The audience is subscribing to the theatre, more so than any particular slate of productions because they trust that the theatre will present material that they find worthwhile in one way or another. If the theatre breaks that trust enough, that's when the audiences will start going elsewhere.
One of the great things about New York is that you have institutional theatres to fit every sensibility...places that present almost entirely new work, places that present almost entirely revivals of known work, and places that do a mixture, so, if your favorite company starts letting you down, you have plenty of choice if you decide to go elsewhere.