As a one time poet (wasn't doing it as a profession, but I have had a few things published and one long piece used in a fund raising campaign) I should point out that “ballad” simply refers to a poem that tells a story - with or without music.
Combining “ballad with “rock” into a compound term can be more problematic, and it becomes likely that perceived meanings of the resultant term are regional.
That said, Marty Robins and Johnny Cash and Red Sovine may have been masters of ballads, but I can't see any way to think of them as rock. And even though Gordon Lightfoot gets a lot of play on rock stations, I wouldn't call his music rock either, its more pop.
Terry Jack's self recorded ballad “Seasons In The Sun” is both a ballad and rock though, and most of the songs from Jethro Tull are in fact ballads if you examine the lyrics.
The Moody Blues had some good ballads as well.
Some of the best rock ballads tell simple stories, such as Creedence’s Sweet Hitchhiker.”
At any rate, what I actually meant to do before going down the rabbit hole was to suggest seeing if you might get together with Kathy In Alaska and the folks who run the Freeper Canteen and revisit these last few music threads over where more music fans will jump in.
Can't argue with the origin of ballad as in poetry. You are correct. However, like many English words it has experienced an expanded definition and now includes a music genre. Again, think Sinatra, Bennett, Martin, et al to begin.
If we can agree on that expanded definition, maybe we can agree on the further definition of "power ballad".
I am a drummer, have been a rhythm guitar player, sung back-up vocal, and eventually lead vocal/front man in numerous bands. I even wrote some originals, although they didn't get published. I know something about tempo and musical genres and can still read sheet charts. I started listening to Strauss, Beethoven, and Elvis at 5 years old in 1955. Later, enjoyed Wes Montgomery, Jimmy Smith, Coltrane and more obscure musicians like Gabor Szabo.
Want to quiz me on the beat of any music genre? I'll start with the Waltz which is 2/3 timing. Shall I go on with 1/2, 3/4 etc. Should I pull out my old Metronome or just state what I already know?
From my perspective, Power Ballads have a moderately slow to slow tempo (speed for those who don't understand tempo). The guitarists usually use what is known as power chords or power fingering on the frets. The bass and drums are usually very heavy sounding and prominent in the mix, but not always. Like poetry, the lyrics can be anything. The melody is usually, well, melodic.
Look through this thread for examples of power ballads. Some are right on, some are close, others are just simple ballads and others are just favorites. Yes, power ballads can be subjective, but I know them when I hear them without Google or Rolling Stone magazine to tell me.