Yeah if we want to focus strictly on regular season production, he's right there.
Lets look at the top 10 players in RS production over the last 5 years (Panarin's time as a Ranger) and see how they've performed in the playoffs relative to their RS production. I'll save everyone (and myself) the trouble and just flat out tell you that both McDavid, Draisaitl and MacKinnon(1 2 and 3 on the RS list) produce at a higher rate in the playoffs than they do in the regular season - Those guys are the elite of the elite and it carries over even more so when the chips are down.
Panarin - 1.32 PPG to .76 ( -0.56 PPG)
Matthews - 1.27 to .98 (- 0.29 PPG)
Pastrnak - 1.25 to .92 (- 0.33 PPG)
Marner - 1.24 to .78 (- 0.46 PPG)
Kucherov - 1.48 to 1.29 (-0.19 PPG)
Rantanen - 1.23 to 1.32 (+0.09 PPG)
Tkachuk - 1.10 to .94 (-0.16 PPG)
Panarin's drop of is more drastic than everyone else and even taking the drop off out of consideration, he's been a substantially weaker producer than everyone else in the top 10 outside of Marner who is within range. The same Marner who has been getting destroyed left and right by the media/fans.
Mika has gotten way more heat than Panarin (and I'm not saying that he should be shielded from it, he shouldn't) but in the last 5 years - 1.03 to 1.00 (-.03 PPG)
We could push this exercise to the top 20 and it wouldn't change a thing. Even if we went to just raw ppg, he'd be 20th out of 20. Not something you want our of the 4th highest paid player in the league.
Big paychecks bring big expectations and playoff performance matters. He's fallen short there by a lot and is one of the biggest reasons this team hasn't been able to get over the hump.