He also taught that ALL OF THE ANCIENT FATHERS agreed with his opinion on heretic popes.
Has this been verified? It would seem stupid of multiple theolgians to argue against the Church Fathers - doesn't make sense. The only logical answer is that +Bellarmine's view agrees with the Church Fathers "from a certain perspective".
There are MULTIPLE perspectives and angles to this topic. He obviously didn't convince everyone on every perspective, nor did the Church Fathers speak on every perspective, therefore theolgians continued to debate.
Finally, just because +Bellarmine is a Doctor, doesn't give a 'rubber stamp' to all his writings. As we know, St Thomas was partially incorrect on the Immaculate Conception.