Even setting aside what Kyrie's stats / usage might be on a team without LeBron, I think Isaiah has become a much more well rounded scorer and playmaker than Kyrie.
Kyrie, to me, is Deluxe Jamal Crawford. Isaiah is more than just a high usage isolation scorer.
I would also agree that Horford is more valuable than Kevin Love because of his defense and playmaking.
What we've seen Horford do for the Celts this year demonstrates, I think, why the Celts were so intersted in Love.
Horford is obviously not the rebounder that Love is, but I think he's better at scoring 1-on-1 inside against smaller or slower big men (e.g. Gortat), and he's a better passer and defender.