KUSHIDA had already done everything he could do in New Japan and was 100% being phased out into BUSHI status within a year or two when he left.
Yeah, he floundered in WWE, but there's theoretically a 0.05% chance he could have made it into a really big spot if everything played out right. And whatever the case I imagine he probably got paid very well in his stay.
And now, it's possible he returns to New Japan in a much better position than he would be if he stayed there the whole time. I don't know, I'm just speculating. But it's possible that tomorrow he shows up to challenge whoever wins Hiromu VS Ishimori. Which, again, I am very confident is a much higher position than he'd be in if he stayed.
I think KUSHIDA played his cards right.