Yep. A diamond is basically a really really expensive mirror. The mirror is made out of all the facets on it interacting together and reflecting back and forth and out the top of the stone back at you- the viewer. That's what makes it sparkle. So if the cutter cheats and is trying to save material to make it weigh more on paper, or make it flat and shallow but have a wide diameter for its weight, then that can interfere with sparkle.
There is a set of variables which forms the basis for diamond pricing and all of the above factor in to it. So a stone that is beautifully cut and in a desirable color range and clarity range (and a cert from a reputable lab) is priced much higher than a stone that has a less desirable color, poor clarity, and bad cut optics or a cert from a questionable lab. The lower those go, the cheaper the stone and the more you find them in cheaper jewelry as opposed to high end jewelry.
(Wait- I really do have a point)
Last I looked (when we were looking for my engagement ring), the actual lab grown diamonds maxed out in size (around 1ct or so because that's as big as they could grow them) and their price was around 20% cheaper than a mined stone. However, IMO once you factor in that the cutters may or may not be paying attention to good proportions, and that GIA and AGS won't grade lab create stones, so the color and clarity listed on whatever cert they come with may or may not be accurate, it doesn't seem like much saving to me. (If GIA or AGS as the most trustworthy grading labs change their mind and starts issuing certs for lab stones, I'm all on board).
So, at the moment I am applying the same logic to whatever DeBeers is scheming. To me $400 for .25ctw of mediocre or poorly cut material doesn't seem like that much of a deal, so I'd wait and see what the stone quality will be like. Will it be as pretty as the promo pics? Or, really will it be like getting the crummy industrial D grade stuff they put in jewelry "promo" products? Time will tell, I suppose.