Jesus did not say our unleavened bread had to be made from wheat or it would not be accepted, if it had been an order he would have clarified it....he did not. So therefore 'unleavened is key' not the flour used.
And since when is a rice cake a type of "flour?" If you want to get completely away from flour, then it would be just as rational to consecrate a cucumber slice or a Reese's Piece.
"Jesus did not say our unleavened bread had to be made from wheat"
He didn't need to! Unleavened bread, in the biblical understanding of the term, IS made of wheat.
It's the IS that is the issue.
I don't know how powerful you think we think the Pope is - but he is really not as powerful as you seem to think he is.
He can't change the IS of anything so that at one moment it IS one thing and the next it IS something else, apart from his participation in the Eucharist when, acting in the person of Christ, the IS of the bread and the IS of the wine is changed into the Body and Blood of Christ.
Even then, it is not the Pope or the priest who changes the IS, but it is Christ and His power acting in them.
The Pope is certainly not able to change the IS of rice cakes to make them into the IS of bread. Or the IS of grape juice into the IS of wine.
He has no power to change the IS of a falsehood into the IS of a truth. He is just as bound by the natural law as we all are.
You seem to ascribe much greater powers to the hierarchy of the Catholic Church than any Catholic believes in!!!
No, the key is Tradition itself and the authority of the Church to determine these matters. Much of what Jesus intended was not incorporated into Scripture, but was transmitted orally by the apostles and then the Church Fathers and so on.