This is on par with saying that Black Clover should not have magic, Dragon Ball should not have ki, MHA should not have quirks or One Piece should not have pirates.
Spiritualism/mysticism/myth/whatever you want to call it has been a core part of Kingdom since the beginning of the series. To say that Kingdom should not have it is not judging the series for what it is but judging it for what it is not, which is just a plain unfair thing to do.
The concept of life force has been around in the series since Chapter 85
The technique used was alluded to earlier in this very arc
All of this was done by the character who has the strongest connection to spiritualism out of any character in a series full of spiritualism.
So it is not nonsensical. Perhaps not cleanly executed but certainly not nonsensical.