We've been over this many times. Mercer started in the top-6. He played himself out of the top-6. At Thanksgiving he was 2nd only to Bratt in both total TOI and ES TOI among forwards, yet had 4 points in 17 games. That's fewer than Holtz, McLeod, Lazar, and tied with Siegenthaler.
Even if he's "buried on the 4th line," which he wasn't, but even if he was, then why were the other 4th liners outproducing him? When Jack and Nico went down he was supposed to be the one to step up and replace their offense and he failed miserably at it.
In terms of points/60, he was 408 out of 425 forwards who recorded at least one 5v5 point.
He was one of the worst forwards in the league the first 20 games of the season and would have been healthy scratched if Ruff actually had the balls to break his iron man streak.
Go ahead and make excuses for your favorites if you want, but you don't get to re-write history. The numbers speak for themselves.