From my reading of it what I think the premise is has nothing to do with bell curves and flat line probabilities and everything to do with outcomes in RPGs. I believe the primary conclusion they are making is that flat or curved probabilities makes no difference when the target numbers are appropriately set. In other words if you want a 50% change of success and set a TN around 11 with 3d6 or set it to 1-50 on a single d100 roll then you’ll get what you are looking for. I think the suggestion is that the whole bell-curve -v- flat probability ends up just being a red herring on how a roll comes up because if the final outcome ends up being the same based on how you set the target then it really doesn’t matter which method you use. Sure, if folks FEEL they need the bell curve for some reason, the that’s cool, go with that, but in the end it’s probably just a wash compared to what you are effectively looking for in the final outcome so long as that outcome is aimed to the roll type, so in that sense the “swinginess” ends up simply being irrelevant. Yes, 3d6 are less “swingy” than a straight percentile in the roll, but the roll is not the relevant part, it’s the outcome you are concerned with, after all.
That’s what it looked they were saying to me, anyway. (And I am definitely no math major, or anything).