Increasing the price point is only a mistake if it's due to a feature that does not qualify as a selling point. Since 3D has proven itself so clearly as a burden, its exclusion from Switch was a no-brainer. This is about the premise of your thread: Your claim is that the sales numbers of the 3DS prove that 3D was a good vision, forward-thinking or whatever other positive description you can come up with. But all of the evidence that stems from 3DS sales numbers points to 3D being a great liability. Hence why I say that the 3DS's ultimately solid lifetime sales are not because of 3D, but in spite of 3D.
Switch doesn't need to sell DS numbers to prove that "mobile killing handheld" is untrue. At 100m Switch consoles sold it will already be undeniably that Nintendo self-inflicted damage on their handheld market with the 3D feature of the 3DS. At 125m Switch consoles sold it will be undeniable that the main culprit for Nintendo's decline was Nintendo themselves. At 150m it merely means that "mobile is killing handheld" has little to no ground to stand on anymore, so the argument could be expected to simply die off.
DVD playback was considered a feature of 6th gen consoles. The Panasonic GameCube, which could play DVD's sold worse than the standard GameCube which couldn't play DVD's. The higher price point created a negative against what was a desirable feature at the time.