Poehling is clearly ahead of Kotka when it comes to NHL readiness...
Don't know why it's always a competition between the two but I'll play.
I think some people are confusing physical maturity with NHL readiness.
Kotkaniemi having a year of play (and excelling) against pros under his belt goes a long way.
More importantly, let's say they're both given a top 6 role with PP, I'd have no hesitation saying Jesperi would have the bigger impact. Because of one reason - he's simply a superior talent.
While Poehling could be the more physically-advanced player, Kotkaniemi possesses the more developed mental faculties, already being at an elite stage for his age. That's not to mention every other tool besides skating and strength where he's sharper.