I have always played in covers bands where an MD of sorts has picked new material - sometimes there was a joint MD.
The band I play with currently is run as a complete democracy, meaning that everyone has an opinion about new songs. Inevitably, this results in numerous different suggestions for direction, which ends up with any decision taking weeks if not months and very often not being made at all.
In my opinion, placing the responsibility for adding new material, arranging, directing is much better handled solely by whoever is the most qualified and experienced in the genre in question.