PageRank is almost certainly only a signal used in a learned model. An important signal, but probably one feature in hundreds, if not thousands. It was a critical algorithm to helping them overcome Yahoo in the 90's, but I doubt it is as essential these days.
What is the most important signal? Click-throughs. This is why any new search engine is at a massive disadvantage.
What is the most important signal? Click-throughs. This is why any new search engine is at a massive disadvantage.