Let me just preface saying I never watched Kovalchuk so I only have his stats to go off of, if I’m wrong feel free to correct me:
Kovalchuks best season was either 03-04 or 11-12
In 03-04 he had 87 in 81, won the rocket (tied totals with 2 others), 2nd in points and 8th in PPG but a couple guys only played 40ish games, and finally 10th in the hart. The impressive fact was that he outscored his second best teammate by 32 points and 21 goals. The team as a whole was not good, as they were 20th in the league in standings
In 11-12 he had 83 in 77, came 6th in rocket, 5th in points and 5th in PPG (Crosby only played 20ish games), and finally 10th in hart again. Gap between teammates wasn't as impressive as he had a 5 point game and 11 goal gap. The team was solid and made the playoffs as WC but were 8th in the league. Again he was good in the playoffs leading the team by 4 points and tied for scoring on his team, 3rd in the league in points too,
from the stats it's close but 03-04 Kovalchuk looks like his peak form, he outpaced his teammates by an absurd rate and was a goal scoring machine.
Pastrnak's best season is either 19-20 or 22-23
In 19-20 he had 95 in 70, won the rocket (tied with Ovi), tied 3rd in points and 4th in PPG and 4th in hart. He outscored his second teammate by 18 points but 17 goals. The team won the presidents trophy and he was alright in the playoffs with 10 in 10.
In 22-23 he had 113 in 82, came 2nd in rocket, 4th in points and T-4th in ppg and 2nd in hart. He outpaced second place on his team by 46 points and 34 goals. The team was next level as they were one of the best regular season teams of all time....but then the playoffs happened where he scored goals but didn't do much else.
If pastrnak had won a cup or even had an elite playoff run in either I think I'd vote him pretty easily for peak, but since both years he wasn't amazing I think it becomes closer. I'm gonna go homer vote and say pastrnak since I've watched him and how he tears the leafs apart and he has done the same stuff regular season wise as kovalchuk but gotten higher in the hart voting.