Another reason I like the problem theatre/action storming approach is it's good example of moving to a peer-to-peer model of working with groups. If I'm the coach/trainer, I do play a role holding space, but I am absolutely not cast as an expert with the answers. As I said in an earlier post, I will often volunteer wacky solutions partly to reinforce that I am not the authority figure here.
There is a big financial incentive for trainers to peddle top-down content-led training. It makes them the star and helps justify a fat fee. Fancy manuals and proven theories are very reassuring for buyers. But I don't think it's the cutting edge for the really difficult challenges. For those, you need to find ways to really engage people and get them collaborating, during and after any workshop, in an exploration of what's possible.