Tatar saw a notable improvement upon leaving. 58 points in 80 games, then 61 points in 68 games. Mostly playing with Domi and Danault if I remember correctly.
Under Blashill in Detroit he had 45, 46, 34 and 28 points.
Nyquist left to play 3rd line on San Jose during their playoff run in 2019 then joined CBJ who at the time were not very good offensively. He replaced Panarin on PLD's wing, I believe. He was still 2nd in scoring on a team that barely scored more than the historically bad Red Wings. The year before he signed as an unrestricted free agent in CBJ he had 60 points. I think that might be the UFA production bump.
Also he missed all of last season, so that may be why he produced zero points.
You're being a bit misleading about Mantha. 4 in 14 REGULAR season games. Playoffs are different. And on that matter the whole team pooped the bed but Mantha was one of the few Caps players that looked like he gave a shit on the ice.
And it's already been proven that AA's 30 goal season was an outlier when he was playing second line minutes. He's producing at around 0.50 ppg just about every other year except for his rookie season. Don't go full MBH on us here, my dude.
I think there are a few reasons why our offense was amongst the worst in the league over the previous 4 seasons.
1 is that our defensemen haven't been able to stop a forecheck or break out of the zone cleanly so Detroit spends way too much time in their own zone.
2 The overall lack of depth scoring from the 3rd and 4th lines as well as a total lack of offense from the defense. (See point 1)
3 Bad defensemen. (see points 1 and 2)
4 Coaching not being able to make adjustments to mitigate the disaster in our end.
5 Coaching style: Blashill loves his low impact hockey. He loves when defensemen chip it off the glass because if we can't get it, neither can the other team. And he loves just dumping the puck in the corner! Except he forgets to tell Detroit's forwards that they have to go in after it.
6 Management (Holland) spending money on some of the absolute players he could have spent money on. (See points 1 through 3 again.)
I'm not a Blashill fan at all but I won't 100% blame him completely for the train wreck we had from 2017 to 2021, but he has to bear some of that responsibility.