If you had no knowledge of his history, you would see how empty and meaningless his work is without it. It only has content because critics and art historians have imbued it with Rothko's personal angst. Without that, it doesn't stand on it's own.
It's just blocks of color, done repetitively. Like Jack Nickolsen's character in The Shining typed "all work and no play make jack a dull boy", over and over. In itself, and without knowing that it was created by a madman, the words have no value. So also with Rothko's works.
Well, that's it then. You're right and I'm wrong. Feel free to burn all the Rothkos because you hate them. Yawn.
Perhaps with Newman, you might be able to say that about his zips. But I have never seen two identical Rothkos.
Challenge: find two Rothkos that are EXACTLY alike, and I'll concede you your point that he did just repeat himself. Hit Google, Image, Rothko and see what you get.