Indignation? My degree is CompLit from Fordham. It’s broader than English Lit but we managed to delve deeply enough into American writers to know about Cather and her work (those damn, thorough Jesuits). She was an important writer, not some second rate hack who should be ignored. I am genuinely surprised by your lack of knowledge of her...surprised, not indignant.
There are plenty of important writers I've never read, and no doubt the same is true of yourself. That's one of the great things about literature...there's just way too much of it to master.
What the lifelong student of literature can achieve, with dedication and hard work, is a sort of survey, with a working knowledge of his or her specific field of study.
Clearly you believe that every student of literature in English should have read Cather. I think every student of literature in English should have read Kipling. I'm not sure either of us has exactly cornered the canon, if you will.