I suspect any of could put together a set list to keep everyone happy for one evening. Where the need for knowledge comes in is to be able to pull that off every week.
Of course. A DJ, but also an algorithm, can choose from top tandas of the top orchestras, take the top 5 orchestras twice, balance instrumental and sung, sort them according to time and structure, and a 5-hour playlist is ready. In my opinion, the result is quite usable; many DJs work this way, consciously or unconsciously, me too.
However, the result is somehow boring, and how a DJ deals with this boredom - even personal boredom - makes the difference. Simply putting up with it is often not a bad solution.
Still, when I look at my shortlist for the next milonga, it doesn't look like this:
Vals: Julio De Caro, Ángel D'Agostino, Héctor Varela, Sexteto Cristal, Donato Racciatti
Milonga: Lucio Demare/Ángel Sica/Ángel D'Agostino, Cuarteto SolTango, Alex Krebs, Sexteto Cristal