Kenpachi isn`t the strongest Taicho.
His Reiatsu ist the strongest, but he don`t have a clue about Demon Magic and so on.
I bet, Byakuya and some others would waste him
They simply don`t fight him because he is a psycho
Ichigos attack in the Ken-chan vs Ichy fight, was maybee a stronger Version of Ichys shikai Attack.
Maybee he will learn it someday from Zangetsu?