You need to stop reading and ride. Seriously. The difference in weight of a 650b Stans Arch EX wheelset and a 29r Stans Arch EX wheelset is exactly 100 grams which, according to you is insignificant. And if either of them is flexy to you, you need to lose weight. And a 29r will not have a larger contact patch. The size (square inches) is determined by the pressure you run and how much you weigh. The shape is different on the larger wheel, but they are the same size.
As for harder to accelerate, it isn't about rollout is about having more mass further away from the center. It's physics. Look it up in a book. Now, the larger wheels will also carry more momentum and roll over roots better. Again, physics.
I've been riding 29rs for almost ten years now. From tight and twisty with punchy climbs to rough descents. On rooty trails 29rs make a big difference, if the trails are rocky (square edged rocks) the difference is less noticeable. And the more suspension travel you add the less the wheel size makes a difference. But for a hardtail? There is a reason 29rs took over that market as soon as there was a decent fork available (I. E. When Rock Shox started making the Reba 29)