His underlying numbers were crap though.
His shooting % numbers were through the roof.
History says that he will come back to earth this season. We will know in a few months.
What kind of "underlying numbers"?
Don't just throw random words out and not back them up with figures to at least show some context.
Playoffs at 5v5:
Offensive start% 29.41% (lowest on the team)
Offensive zone faceoff% 27.45% (lowest on the team)
Corsi% 51.55%... above water and considering his zone usage... solid number.
Fenwick% 48.74%... slightly below water but again considering his zone usage.. not a bad result.
Shot% 44.05%... again this is pretty much expected with his zone usage. Not a terrible result.
Scoring chances% 55.26%... shows that while he was on the ice the team out chanced the opposition.. not something you'd expect if he was that terrible defensively.
High danger chances% 50.00%... again not a bad number considering he had a grand total of 14 offensive zone faceoffs vs 37 defensive zone faceoffs in the entire playoffs. That's objectively pretty slanted zone starts if anyone is being non-biased.
Bjugstad also had sub 50% numbers in all these categories as well... and he had very tough zone usage as well.... offensive zone start 38.24% and offensive zone faceoff % 32.14.
These players weren't getting any prime offensive time and they still managed to pot 3 goals each at evens... outscoring everyone at evens not named Leon Draisaitl.
It's a GOOD THING to be able to step up and perform well under pressure and actually contribute offensively... and that's what both Kostin and Bjugstad did under tough circumstances with the zone starts and minutes they had.
As an aside... Bjugstad and Kostin were 2nd and 3rd respectively on the entire team in hits which was pretty impressive given the minutes they played.
RNH 160 minutes at 5v5 1 goal
Kane 208 minutes at 5v5 1 goal (yes I realize he was still recovering from injury which helps explain some of that underperformance)
Yamo 159 minutes at 5v5 1 goal
Hyman 176 minutes at 5v5 1 goal
These were top 6 players getting time playing with McDrai and they were collectively outscored by Bjugstad and Kostin. They had tougher comp as well so that's context as well... but you don't take away the 6 goals that Kostin/Bjugstad scored just because you say they were "lucky" and shot well... umm that's the point of the playoffs... the players are supposed to step up and play well and that's the reason a team moves on... overachieving when it counts the most. Not enough Oilers actually did that and that's a big part of the reason why their journey ended in the 2nd round.
Let's say even 2 or 3 of RNH/Kane/Yamo/Hyman would have each potted a couple extra goals like Kostin/Bjugstad at 5v5... the Oilers likely would have moved on instead of going down in 6 like they did.
Kostin is gone sure and we all move on... but it's revisionist and biased to say he sucked defensively and got "lucky". The stats don't support that he sucked defensively and his goals count just as much as anyone else who scored goals. It's safe to say others needed to step up and be a little "luckier" as well in the minutes they played (in some cases 70/80/100 more minutes at 5v5 than the 89 minutes Kostin got at 5v5).