Just a reminder. You're all saying how Kenpachi was beaten by Juha Bach/Emperor ... wrong.
He was beaten by Royd, the Quincy that copied Juha Bach's appearance. And he won't be the strongest shinigami.
And when someone pointed that Ichigo is a human and therefore he can't be the strongest...it's exactly the reason why he'll be the strongest, his human heart is one of the main sources of his strength, along with his resolve, will and some stuff that haven't been explained yet.