1-For years, the biggest part of Nylander 5v5 production is coming off the rush, creating scoring chance with his speed. He will not get more breakaway or 2v1 playing with Matthews.
2- personally i would not call it a 3rd line... For me its just 3 different line to help the team to be even more dangerous, especially when you see secondary scoring had been trash all year long so creating 3 line able to contribute, it would just be great so exemple one night matthews line doesn't play well, The nylander would not have all the pressure to carry the team like its actually the case and most of the time that's doesn't work and leafs losing those game.
By spliting all 3. If matthews line struggle, you still having marner line and Nylander line who can overcome it.
3-Florida when they reach their 1st stanley cup, Tkachuk was playing with Nick Cousins s big part of playoff and had his best carreer playoff.
When Kessel was in race for conn smythe, he was playing with Bonino and hagelin, probably the worst line in paper he ever played in playoff.
So playing with non-sexy player doesn't necessairly mean that will make Nylander worst or whatever