It sounds like what he's doing is providing material support for artists (many of whom would not otherwise be able to pursue art full time) as well as connections to collectors. In exchange he buys up the art for very cheap.
I think they're making an argument that he's creating a lot of hype around these artists and that this creates a bubble for their work which bursts after a few years. Maybe that's a reasonable criticism, but it's not clear to me why someone whose work was very popular for a few years couldn't then parlay the connections that they've made and the lessons that they've learned into a reasonably successful career, even if the value of the work declines dramatically from the peak. It doesn't seem like an unreasonable deal to make, especially when you consider how incredibly hard it is for artists to get any kind of attention in the first place.
I'll admit that I really don't understand how the art world works, despite the fact that my Mom is a professional artist.