Do we give 100 teams a task to accomplish in Lisp, but tell 50 of them that they can't write their own macros? Or tell 50 of them that they can't use continuations?
If continuations correlated negatively with success, how would we know whether continuations are "too powerful," or merely "poorly designed?" (There is a lot of talk these days about whether continuations are a "Turing Tar Pit" and that a better mechanism needs to be invented)
Or perhaps our 100 programmers are merely unfamiliar with them, and as a result don't use the features well?
My feeling when I consider thought experiments like this is that it is very difficult to define expressions like "too powerful" with precision. This imprecision leads to the effect where we twist our explanations to suit ur biases.
So if we think Lisp is "too powerful" and that it failed in some sense, the lack of precision around "power" and "failure" allow us to draw whatever conclusion we like about the relationship between the terms.