That doesn't prove anything.
Enma has no other function other than taking haki and releasing it. It adds no extra power of its own.
Yet Zoro himself says he would get stronger through using it? Are we really going argue the words of the main guy using the blade?
Not to mention Zoro after Zoro failed to put decent on Kaido clearly says he need to unleash more of enma which in fact at every point after that Zoro was capable of landing much greater damage on Kaido!
Plus BM and Kaido acknowledging the blade’s threat/abnormality.
How obvious does that have to be? Enma is the kind of PU that requires training and mastery and not an instant buff like Sanji’s exoskeleton.