Am I the only one who thinks Helena's portrayal of Bellatrix is cheesy, over the top, and childish?

Everyone who reads a book has their own vision of what the character looks and sounds like. Jo Rowling was on the set and seemed to approve Helena's interpretation of the character. Since she didn't object, I have to assume that Helena's Bellatrix was a good approximation of the way Jo envisioned her. As the creator, she has final say. Sorry it didn't match your expectations, though.