The odds of a second rounder playing in the NHL (more than 200 games) is sub 20%.
I think I'll take Kaapo Kakko.
This is the wrong way to think about it, imo.
"Someone" is going to play in the games regardless. Whether it's a 2nd round pick, some other draft pick, a free agent signing, a player acquired via trade or some guy picked up from waivers.
Kakko has already played 5 years and based on his current contract, his qualifying offer is for $2.4 million. He also has the ability to elect for arbitration at some point before hitting unrestricted free agency.
For a team in the Hawks position, he's not the worst kind of guy to bring in for nothing, but a high 2nd carries a good bit of upside to get a player that if he really hits can outperform his contract while the Hawks are in a competitive window. If Kakko gets on track, he's likely approaching UFA when the Hawks are in a competitive window and likely to be at least moderately expensive, and at that point, is he noticeably better than filling the roster spot and cap hit with some comparable player (with the added benefit of having a better idea where exactly your true needs are based on what emerges out of your pool of draft picks)? There will always be 2nd round picks to trade away for someone in the future...
Kakko being likely better than a high 2nd is fairly irrelevant unless he's also noticeably better than filling the spot he would otherwise occupy over the next 5-6 years with the next best alternative approach. Or else you just traded something that could carry a high upside for nothing.