Of course, DS was crazy back then. I'm not saying that Switch could sustain such high sales all year long but that in this period, if supply was there, Switch could have definitely seen 150k+ units on a weekly basis, like DS in 2006.
PS4 userbase doesn't disappear overnight. PS4 is still a popular platform among jRPG gamers (after all, mainline FF and DQ are there). Hence, PS4 still carries some weight in total sales for such games, like Trials of Mana. The fact that Switch has a higher userbase doesn't matter much in the end given the genre. A life-sim? A platform? A party game? Sales on Switch would be definitely much higher. A jRPG? Sales across the two platforms will be much more similar.
In fact, I'm surprised that Switch version is so close. We all remember multiplatform jRPG or anime games from 3DS-PSV or Wii-PS3 era and how those sold on Nintendo platforms. Switch is a huge improvement. Adding to that, we have seen how Western markets tend to favor Switch for this type of releases. Overall, the result is super-positive. In fact, I'm expecting by the end of the year most of multiplatform games to sell better on Switch FW and LTD as well.