While your argument is not without some merit, it has problems too. It pretty much says that we need more data to draw strong conclusions, which is true. But on the other hand, manufacturers, publishers and developers can't wait around for a decade to find out what they should do today. They have to lick their finger, stick it in the air and try to estimate where the wind is blowing and how fast. And the one big certain trend is the growth of mobile platforms.That's not a trend. A trend in consoles would have to be charted across several generations. Otherwise people could have looked at Wii and concluded that N.'s next console would sell 200 million... With only two reference points you've no idea if one of them lies on the trending curve or is an anomaly. Looking at all Nintendo's consoles, there's a very clear downward trend with Wii just being anomalous.
(I'll add that I wouldn't even expect such obvious trends as I'd have thought ongoing adaptation would result in different products with different levels of success. It's only Nintendo of the current players that has this definite market-share erosion going on. The other guys have platforms that are hit or miss per platform, no trends.)
The presense of a strong dominating trend makes it difficult to estimate other market forces, whose influence gets overwhelmed in the overall picture. So in this case, even though dedicated gaming platforms are declining in the marketplace, if you want to launch one anyway, then it is arguably harder to see just what is required to build a sustainable business around such a platform of if indeed it is possible at all.
It may be that the CEO of Ubisoft will turn out to be correct - that the NX will help the industry grow and pull back some of the casual audience. He may also turn out to be dead wrong. But if you are a publisher, you have to decide now whether you will invest in trying to strengthen such a platform, or if you should spend those funds hedging your bets on iOS instead.