I'd start by saying the picks make it a no deal IMO
For next season Mercer and a 1st for Nylander would be my limit but, Mercer is younger, more of a 2way player and steadily improving and his contract the year after will be cheaper than Nylander's
Since NJD are so young I'd stick it out and wait for Mercer to continue his development.

Second and third are for retention

The problem isn't his contract this year. It is his next contract.

NJ isn't doing this.

NJ isn't giving up Mercer by himself, there's no way they give him up with a first round pick

If Leafs add Knies they'd might have shot at getting this done but man, Mercer is a fair bit more valuable than Nylander on his own, even at 50% retention.
It's kinda common knowledge that top 6 fwds still on ELCs carry more value than pending UFA wingers

Not when the player is miles better than the other

Why are we so in love with Nylander to NJ... Why are we rushing for a cup. Brainless ppl out here man. Can we plz move on from this clowery

Nylander, Age 21 Season: 82 GP, 20G, 41A, 61 Pts. Average Time on Ice: 16:41. Point Share: 6.7
Mercer, Age 21 Season: 82 GP, 27G, 29A, 56 Pts. Average Time on Ice: 16:34. Point Share: 6.4

Struggling to see where you draw this conclusion from.