Finding him on the PP is not the same thing as finding him at full strength.
Stating that he is point per game over the last 8 is certainly accurate, but does not tell the whole tale. 5 of the 8 points have been on the power play. One of the goals came on a 3 on 3 in OT. That leaves 3 ES points in 8 games. Sure, all of the goals and assists count. But I would expect a bit more production at ES before pounding the chest and wanting to staple him to the top line. Like I said, largely this managment gives the kids bigger roles when the a) earn it & b) show that they are ready for it. Just my view, but that is not where Kakko is at.
Development is a long term thing. Playing him on the top line is not going to hurt or help his development, looking at it big picture wise. What it can do is hurt his confidence if he is not ready for it, just as his confidence is growing. I have no doubt that he will get there, but also do not see what he has done so far to demand that spot. Heck, Buchnevich has done more to deserve it than Kakko has.
Trending upwards in some aspects, but not all. And until he has improvement in the others, I doubt management is going to do as you suggest. But what do I know? I am just a speculating fan.