I'm going to knock this one out at the premise on which your whole argument sits.
For your post to be of any contradiction against mine, you'd have to demonstrate that the demand isn't there.
The Switch is selling quite well, and with an already healthy 2019 lineup announced with headlines like Pokemon coming up in 2019, there is no reason to think that consumer demand won't continue to be there, and high; and it's evident for any retail chains that this is the case.
Well, I can't demonstrate that the demand isn't there, because the sales figures for December 2018 have yet to be finalized by every tracker on this planet. All I can do is extrapolate from the figures we do have and it's not looking like Switch will sell through 11m+ in Q3 of this fiscal year. It needs such high sales, because otherwise Q4 will see a correction in the form of lower shipments in case that NIntendo ships 11m+ units in Q3. If Nintendo doesn't manage to ship 11m+ in Q3 (again, because retailers aren't placing orders for that many units), then Q4 will need shipments of 4m+ which would be a significant year over year increase. We have yet to learn the full release schedule for Q4, but it's doubtful that there will be any huge hardware movers added to the already known NSMBU Deluxe.
Which is the quarter in question - Q3 - holiday season, manufacturing is the only thing stoping Nintendo from not shipping intended consoles in Q3. And as I said Nintendo didnt lower their forecast before Q3 since they believed in their forecast, they have talks with retailers all year about their expectations, they're not going in blind with their own forecast. Clearly both Nintendo and retailers, had faith in what could be sold during the holidays and after which we see now is indeed happening.
As for the second bolded part, clearly you want to be prepared. Dont want to be left hanging in the most important shopping period all year, if it piles you calibrate next quarter however it fits, there were 2 big games in January and February that year for Sony that they clearly were expecting to sell hardware and late shipments in Q3 clearly were intended for. Nintendo has a big game releasing early January that will likely push some hardware which will also need to be shipped in Q3.
Nintendo sticking to their forecast does not give any indication for retailer expectations, so you can't take it for granted that retailers have agreed to buy that many units from Nintendo. Five years ago Nintendo stuck with their 9m forecast for Wii U before the holiday season, so that's a good example that there's no link between Nintendo forecasts and retailer expectations/agreements; said forecast had to be lowered to 2.8m during the following financial report, so Nintendo's belief from three months earlier was not even remotely in the realms of possibility. Nintendo won't be that far off with Switch, but them sticking with their forecast doesn't provide any sort of guarantee other than they have no manufacturing problems. Nintendo still needs retailers to buy those units though.
In the case of the PS4, Q4 has been repeatedly weak because the preceding holiday quarter had retailers overestimate demand for the PS4. Remember, ultimately it's the retailers that dictate the size of shipments.