E' isn't really about avoiding the verb "be". For example, IMHO E' could allow the passive. (I don't like the passive for other reasons.) It could allow us to say "The purpose of E' is X", because that's equivalent to "E' accomplishes X". Any usage of "is" that you could restate without "is", and without introducing new data, is fine.

The bad kind of "is" is the "is" that hides data. When someone says "Hot peppers are nasty", they should instead say, "I don't like hot peppers." When someone says "Jimmy is irrational," they should instead say "Jimmy plays the lottery", or present whatever data they're using to infer that "is".