In a vacuum where team needs/composition, salary cap, role, etc. doesn't matter...yes Nylander is the better player and the guy you take given the choice between he and Kapanen if you are starting a team from scratch and have a choice of one of those two players. Nylander likely has better health and his shooting percentage probably rebounds back to norm and he is a 20-25 goal 60 point guy that plays center.
In the real Blackhawk world where Toews and Strome (unless you think last year was a mirage) seem to be penciled in as your top 2 centers going forward and you still have Anismov on the roster, the Hawks don't need a 7 million a year center. The Hawks need a right handed RW who is defensively responsible, kills penalties, has some grit that they can plug with DCat/Strome and Kapanen is a ridiculously good fit. Kapanen is not some huge physical presence, but with a lineup that has Kane, DCat, Kahun, maybe Sikura, Strome (who better be having a great offseason in the gym), and even Anisimov (despite his stature is a pretty nonphysical) he would add some grit. Hell, Kapanen's 92 hits would have had him 2nd among Hawk forwards last season. Kapanen at 3.5-4 million is a way better fit then Nylander at 7 when DCat and Stromme are likely sniffing that rate and adding to a pretty bloated forward group that already has 10.5, 10.5, 6, & 4.5 committed to 4 guys.