First of all, it's not math, it is fight. I cannot agree with Obito>Itachi, because i don't see Obito's winning here. Senju dna is great boost for Obito but there is something more important than stamina. Mind. In some way Obito is still a child.
About Obito vs Minato. We saw Obito's loosing, but it was a time when he was unexperienced, he just tasted the new powers of him and decided to get his revenge. He was not clearminded guy, how on earth he could win agaist determined guy, who wants to save entire village? But Obito now is probably stronger than his teacher.