I think it’s because Malfurion and Tyrande were great characters in WCIII and competent leaders. Only once they were brought into World of Warcraft did their storylines begin to falter and then plummet.
I assume the people writing the stories are completely different, and the old guard was definitely more skilled at it.
I have to say though, from my observations of the Cataclysm events, I believe the two may be Tyrants and so dissension isn’t an option. While you quest in Teldrassil, you can find some other Night Elves questioning them and what they did with Fandral (who was previously a respected and also beloved Archdruid) but they do so in hushed tones and stop conversing when you approach, which gives the impression that Tyrande’s rule is never to be questioned.