If you've played in bands, you probably know that it rarely works if everyone has an equal input (I'm sure there are a ton of exceptions to this, but IMHO it would only work if everyone in the band is equally talanted as a musician and composer). Now, everyone in DS were good musicians, but it was probably Mark's unique style and fantastic talent that gave them the edge to actually "make it". So, for the band to reach its full potential, it was probably necesary to have Mark at the steering wheel.
As you say, you can never know what he's actually like these days. I honestly believe he's mellower than before, but I don't know. IF he is, then that might have something to do with the fact that he IS the attraction, there is no debate on why people are coming to the show. He probably doesn't need to run things aggressively because everyone knows their place.