You started it, Dave, you coined the phrase "stadium rock" (which to all intents and purposes is the same as "arena rock", right?). And of course musically it defies definition, any band popular enough will play a stadium if it can.
Johnny played the Blues, true. But not all the time and he wasn't a purist. During his 70ies heyday he wasn't any more Blues than his fellow stadium-inhabitants from Foghat were. He fell more into the "virtuoso axeman with backing band"-bracket (similar to Rory Gallager or Alvin Lee/Ten Years After or Robin Trower) and he sure looked the part as well.
None of this takes away anything from his music or your music taste (or mine for that matter, I have nearly all his recorded work through all eras), it just goes to show that "stadium rock" perhaps isn't the most scientifically exact term.
PS: Shania Twain, at the height of her fame, just as Garth Brooks at the height of his would all qualify as "arena acts" ("arena country-flavored pop?") in my book, it's not an insult to me. And both Rush and U2 were/are "arena rock", though their music bears little in common.