Well, that is how they are sold to the public, isn't it?
I do have a couple more comments on this Lead Singer Disease idea. There is one singer I think epitomises it; Bono of U2. I know some on this board like U2 so I should leave it there, except to put it mildly I find him pompous & arrogant.
I think one reason why singers develop a flamboyant style is to be noticed. Their personalities led them to want to be out the front in the first place (although Rod Stewart claims he used to hide behind the amps) and they need to be visible. Remember when the band is playing the instrumental passages, unless a singer plays an instrument himself, he has nothing to do. So he makes up for it when he's singing, so perhaps he can come off a bit egotistical.
Some of my favourite singers play harmonica occasionally; Jagger, Plant, Bryan Ferry. I was surprised when I first saw Roger Daltrey play harmonica; I didn't associate it with him (we have a Blu Ray of the Who performing Quadrophenia plus a couple of big hits & he actually plays acoustic guitar on Who Are You)!
I did have a very big disappointment with a singer's performance & that was when I saw REM. This was the Monster tour so they were on the decline. Michael Stipe came off as a pretentious egomaniac who read his lyrics from a stand. He then tossed the paper into the audience. At the opposite end of the spectrum is Liam Gallagher of Oasis. He just stood there. He doesn't really perform but their sound is so powerful that it worked.