R&R doesn’t accuse sedes of muddling indefectibility with infallibility, but of muddling papal infallibility with papal authority (and of making the distinction between the ordinary and extraordinary magisterium pointless, ...
Take a step back and have a look at what you're saying. Based on your emphasis on strict infallibility, it's theoretically possible for 99% of the Magisterium (the fallible part) to be a total cesspool of error and harmful and leading souls to hell.
If you think that's compatible with Our Lord's promise that the Holy Spirit would guide the Church, then I'm not sure what religion you actually belong to, but it's not the Catholic one.
If 99% of the Magisterium can't be complete nonsense, then how much if it can be: 50%, 10%?
YOU render the NON-INFALLIBLE Magisterium absolutely pointless. It's nothing more than the private opining of the man who happens to have the Papacy as his day job. Pope by day, private doctor by night. In fact, private theologian for 99.9999999% of his papacy and teacher of the Church for the rest of the time, when he happens (if he happens) to make a solemn definition.