I understand your argument though power ballad lines are obscure. suite Madame Blue was a great song. Some consider Lady to be a power ballad but I do not.
Are you talking about Lady In Red (basic ballad) or the fast high energy Layla?
BTW, talking about the tempo of power rock, I'm starting to question Suite Madamn Blue in the power ballad category. It gets quite fast. Power Ballads are moderate to slow tempo.