To make an infallible pronouncement, among other things, a pope must be in union with all the bishops in his infallible pronouncement. What he says outside that stricture is his human opinion which is as good as the next man’s. I suspect Francis is finding out something new to him, that not everybody agrees with him. An environmental encyclical would not be “infallible” in any event but Pope Francis would find himself diminished considerably if his bishops were to dissent and back up their dissent with well reasoned theology and many would do just that. Francis will backpedal a lot.
That is technically not so; either the Pope alone or the episcopal college in unison between themselves and with the Pope may make infallible pronouncements, but it has never happened so far that the pope would make an infallible pronouncement without the agreement of the bishops. For example, if a second Arian controversy would arise, and like in the first one, a majority of bishops would fall into heresy, the Pope could alone. if need be, correct and denounce it, infallibly.
I agree fully about the rest of your post.