Both of them are really good. Let me reverse this and ask you how much Matthew's influences Nylander's success? Also, would John Tavaras influence his success if Nylander was playing right now? Could Nylander put up points on a bad offensive team? Could Nylander handle top defensive pairings every game? We know Pesce can play good defense on a bad team. We don't know if Nylander can put up 60 points on a bad offensive team though.
"Both of them are really good" doesn't answer the question I asked and it' not a slight to Pesce or to Slavin. But I'll respond to your question directly by pointing you to examine Nylander's international career and his developmental career in Sweden and ask you...Is there anything from his statistics that indicates William Nylander, is anything other than a very good offensive forward?
Perhaps he is a product of Matthews, although advanced stats suggest he drives play. Perhaps he's a product of Backstrom when playing internationally or of the Swedish developmental system.What's certain is that Nylander produces at every level and in multiple systems. Perhaps the common denominator is, William Nylander's just a very talented hockey player?
Per your example and my unanswered question, the season Pesce was +23 was also the season Slavin was a +23, while every other player on the Canes roster for 2016-2017 was a minus player except Lee Stempniak at a +2. That indicates that there's an influence one to the other or simply extraordinary chemistry occurring between Pesce and Slavin.
So it's not an incidental question when considering that flanking that +23 season, Pesce was -7 and -6 while Slavin remained a plus player, albeit +1...That indicates to me that the catalyst just might be Jacob Slavin and not Brett Pesce. And that any hypothetical conversation one might have concerning a trade for a Carolina defenceman with William Nylander as a principal going the other way shouldn't be named Brett Pesce, but Jacob Slavin.
But in any event, my strong preference to that effect, is to keep Nylander and kick tires on other potential comparable rather than use a principal piece like Nylander for the apparent lesser of Pesce and Slavin.