I still don’t think he’s a good NHL player... just works in a very specific situation... and I’m not sure that without Tanev the Copp-Lowry line couldn’t be better.
What do you mean exactly by a specific situation? His disruptive speed and forechecking prowess aren't reliant on who he plays with. His hockey IQ might not be much better than your average checking line player, but his speed and his ability to hang onto to the puck for ages in the offensive zone make him quite a valuable asset to have in our bottom six.
Also, his four goals in the playoffs were more than every forward not named Scheifele, Stastny or Laine, and dating back to the regular season he's scored 8 goals in his last 22 games (~30 goal pace which is obviously unsustainable, but it does quantify the progress that I personally see in his game).
Maurice ultimately decided to scratch Copp over Tanev when our season was on the line in Game 5, and while some obviously might not have agreed with that decision, I think it says speaks volumes about how effective Tanev was at times last season.