Where do you rank him among rock frontman?
Second only to Ozzy.
shareI'm no expert, but I think I'd put him in the top ten.
He is (or was) a better singer than Mick Jagger or Freddie Mercury. I his voice is pretty well gone now, but in his day he was an excellent singer, as good a technical singer as you get in Rock, with real power, range, durability, and flexibility, with enough of a rough edge to still sound like a rocker and not a crooner. Its true he didn't reach out from the stage and grab the audience the way the absolute best singers do, but he had so much charisma and sex appeal that he didn't need to.
I don't he's think he's the best technical singer, but I agree with you that it's all about the charisma.
shareWho do you think is a top technical singer, if not Plant?
Personally I think Ann Wilson is the best rock singer of that era, but she definitely didn't have Plant's charisma and sex appeal! However, she held on to her voice for decades longer, and here she is singing "Stairway to Heaven" to Plant himself. You know he was sitting there wondering why the hell where the hell his voice went...
https://www.youtube.com/watch?v=2cZ_EFAmj08
Maybe Steve Marriott. No sex appeal at all though.
https://youtu.be/2tNoSmlnxwQ?t=58
Charisma and sex appeal count for a LOT, which is why Mick Jagger tops most people's list of front men. The man can't sing at all, but he's a GREAT performer, and that's what most people value.
And I wasn't familiar with Steve Marriott, but I don't like what I like in the clip. He's trying to be a power-screamer but he doesn't have the depth, resonance, or power to carry it off (or the sex appeal), so he's screaming shrilly rather than with power, and the best I can say is that he's got style and is more in tune than most. But a good power-screamer like Janis Joplin or Plant could blow him off the stage with one power note.