Both hardware and software matter, and for a week with not one but two huge games releasing, 52k systems sold ain't good. 

Point of view.    We are talking about Japan, you can't expect much more.  It's a special territory.   Good or bad is always related to the specific hardware.   If there's something bad, is the poor appreciation of great home consoles from Japan, and you cannot do that much about it, it's their taste.   Considering the situation, hardware figures are standard, nothing to be surprised.

If I was SE I would’ve made the switch port at any cost! Really good FW for KH3 tho

While I am entirely of the opinion that a lot of these Japanese devs should get their butts onto Switch - not necessarily exclusively but as one of their main platforms - let's not forget that Kingdom Hearts 3 was in development for eons.  It was one of the games using the Luminous Tools :P

So it had understandably fallen into the Final Fantasy XV position of "just get it finished so we can make some money on this venture."  It getting a port anywhere near it's launch wasn't happening.

Smash is 3.32mil sell thru in japan. It already surpassed Splat2 and MHW

(555k digital

Based on past sales in I thought 70-80k was a reasonable expectation for a week with two huge games that are practically exclusives. We've seen PS4 go well over 52k before when big games come out. I don't think the software in this case is to blame as its sold very well, PS4 just isn't that healthy in Japan nowadays.

This is just a theory from me, but I think part of the issue is so many Japanese devs just quit on the idea of pushing home consoles.  A lot of them ran away from doing the proper jump to HD development.  And it's hard to sell a market on these powerful HD graphics power house machines when a lot of the games that appeal to that demographic don't take advantage of the hardware at all.  I mean, think about it.  Monster Hunter, a big IP in Japan, made the proper HD jump...just this year.  They dodged the 7th gen jump by shifting to handhelds, shifted to the 3DS next, did ports from that with only moderate effort to some HD machines.  Only just this year did they make a big, HD game.  

And a lot of other franchises that are big in Japan are similar in this regard.  I am not suggesting Japan should have gone all big-hit-or-bust like several western publishers have.  And I'm not suggesting that massive graphical leaps would make the PS4 sell like the PS2.  But I definitely think the PS4 would be an easier sale if more of what was produced in Japan looked to make ambitious use of the larger, more expensive, more power-consuming, non-portable hardware that is the PS4.  What is the point of investing in that kind of platform if the devs of your preferred genres and franchises aren't going to take advantage of that hardware?