if you don't accept a>b and b>c, you have nothing to say about "therefore a>c"; you can say nothing about it. if you did accept a>b and b>c then you would agree "therefore a>c"

>"I" here implies a center of thinking. There is no center.

"I think", according to you, implies that I implies a center of thinking, and you don't believe that there is a center, so you don't believe "I think" even more than you don't believe "therefore I am". You don't have an opinion about therefore I am.

it doesn't matter about the "existence" in the predicate, because you don't accept the "I" in the subject.