Let me get this straight. Switch sold better because of "pent up demand". That means there was more demand than supply at some point and then when supply came through, sales spiked....and yet when supply remains constant with demand, sales will fall?
OK let me explain it to you, switch could have sold 2 million in 2 months, but because of supply issues, it was selling slowly spreading out in each month and getting a boost each month from day one buyers that couldn't buy one. example super classic, beat ps4, and it could probably beaten ps4 for more months if it wasn't for the holidays, now say 2 million people wanted super classic in north america and it only shipped taht amount in 4 months it would beat ps4 in most months, but if they shipped 2 million, first month, sales will start to fall hard next month. wii in japan is a good example once it hit 10 million in a little over 2 years sales fell of a cliff.
That's not how demand works. It can grow or shrink irrespective of supply.
Also, when Switch hits 10 million in Japan, we can revisit your decreased demand projection.