I just love that this has all come around again 🙂 It's just the same as all the discussions about risers in the mid to late 90s.
FWIW, flat bars are an inherently better design simply because they have fewer bends meaning that for the same weight they'll be stronger or they can be the same strength and lighter.
Flat bars aren't inherently any different to risers – you can get exactly the same position if you play with your stem and where the sweep of the bar is. One of the main differences in the past was that risers tended to have more sweep but the wide flat bars out there currently seem to be taking that on board (eg Salsa, Titec, etc). Of course, to get the same position, you'll need a higher rise stem and that may look a bit crap…
BTW, it was Barry Jaeger wot started the riser bar trend in mtbs.