You wrote:
"He was baptized an Orthodox Christian. Conversion implies rejecting one's faith and accepting another."
He was reconciled to the Church. He didn't reject what was true in Orthodoxy. He accepted the Catholic Church and the faith it teaches as a fuller teaching of the truth.
"IS that what he did? If so, his decision implies that his own faith - the one he was baptized into - was somehow unacceptable."
Unacceptable? Are you kidding? You are completely making things up. He saw the fullness of truth. He wanted that. That doesn't mean Orthodoxy was unacceptable.
"Strange I think. That is why I say he made a political decision."
Nonsense. He, according to everything that is known about him and said by him, chose what is true because he wanted truth and the full truth.
"Church people do that all the time."
Church people? You mean Christians? Are we not Church people? Did Paul not say that we are the Body of Christ, the Church?
"Look---I'm sure he was a nice man. But that does not indicate becoming a "saint"."
No it doesn't. A life of heroic virtue, however, does. He lived a life of heroic virtue. He gave up his title, his fortune, a life of glamour and ease, even the most basic and simple comforts, just so he could be a humble Catholic priest serving his flock. He was holy. If he is canonized it will be for those reasons.
What part of any of that do you not understand?
"He accepted the Catholic Church and the faith it teaches as a fuller teaching of the truth."
You said this: "He accepted the Catholic Church and the faith it teaches as a fuller teaching of the truth."