Everyone seems upset kakashi used kamui twice but tobi cancelled it out before it was complete so I don't believe he was taxed for the chakra.
As for tobi vs minato.... Come on, we saw the results. If tobi had stuck around he would've died.
In tobi's defense, he's not a weak fighter, tho he may not have enough chakra in his incomplete form, he's never lifted a finger unless there's something important he wanted. Tho I do think we need to see more techs to take him more seriously. I miss his personality when he was paired with dedara.
I agree, naruto should move to sage mode at this point, he tapped the yin chakra already and speed worked in minato's case( tho he doesn't know that).
And you readers shouldn't poison the well. If you don't like the series go play halo. It's not perfect but There no way to make everyone happy.