Another interpretation of the good sales of Disgaea 5 Complete could be the rise in the number of fans of the SRPG genre on Nintendo platforms, owing to the success of the 3DS Fire Emblem games at reaching (and retaining) a wider audience of players. Considering how we were promised a Fire Emblem game on the Switch even before the formal launch of the Switch itself, I'd say that some of those fans bought a Switch earlier as a result and were able to buy (quite literally) the only big SRPG on the platform for months - Disgaea 5 Complete.
I have only anecdotal evidence from this forum to back me up, but it ought to be interesting to see whether the success of Fire Emblem has, indeed, raised the sales potential of SRPGs as a whole - which I do hope for.
*sneakily begs people to buy more SRPGs on any platform*
I WON A BET AGAINST AZUREN! WOOOOOOOOOOAAAAAAAAHHHHHHHHHHHHHHHHHHH