716 NHL games before he played for the Rangers beginning when he was 20 y/o.
198 KHL and 322 NHL games before he will play for the Rangers beginning when he was 20 y/o.
Even if the leagues were similarly grueling (doubtful considering travel, level of competition, # games in a season, and size of the ice surface) that's 2.5 seasons worth of GP that Panarin will not have as baggage that BR did. Add the fact that Brad was 31 when he signed here and Artemi will be 28 at the start of the season. Add the fact that while the sport generally is trending younger, that has not affected all players similarly. Elite talents have remained elite well into their 30s across the board. Ancient players are still excelling, albeit as top 6ers rather than superstars, but we're talking 38-42 y/o (Lundqvist, Chara, Williams, Thornton). Many players just last season had some of their best seasons to date as 30+ y/os: Toews, Kane, Wheeler, Crosby, Ovechkin, Giordano, Pavelski, Bergeron, Krejci, Radulov, Yandle, Zuccarelo, Kessel... While the data reveals a trend in productivity, when has it ever accurately predicted the career arch of any individual player. Elite talent (ppg forwards, #1 defensemen, vezina-conversation goaltenders) has flourished of late as 30-35 y/os. Because while the league is trending younger, it is also trending lighter, smaller, faster, and higher-scoring. Moreover, younger players are taking up more minutes, scoring more from the beginning, and taking a lot of attention away from the success that the best players of the last decade and a half are still playing at elite levels well into their 14-15th seasons. 2 of the top 5 scores were 30+. 2/5 goal leaders (including the winner) were 30+. 3/5 norris finalists (including the winner and runner up). 3/5 vezina finalists (including the winner).
It is as pointless to assume Panarin will fail to produce through the length of his contract as to assume he will. To say there isn't ample evidence to suggest he could — at least as much as suggests he couldn't — speculates further than we should be comfortable and without real ground to stand on. There might be three players at his position better than Panarin right now. That's a category of player that general trends do not tend to make the best measures for. Point in case: two of those players players are 31 and 33, respectively.