A. Big part of an election IS to show a mandate for the winner. To show a mandate, you need to have popularity. Or "absolute preference" for a candidate - " I like candidate XYZ too win".
Ranked voting shows only "relative preference" - "I like candidate XYZ more than ABC" but it could very well be that I dislike both.
Thus a winner of a ranked voting cannot assure the voters that he or she has the mandate to govern.
Edit: another way to look at this, the winner of a rank voting system is the least disliked candidate, while a regular voting produces the most popular winner.