That's BS.
Last season (2019-2020), 84 points in 70 games which left him eighth in the league. The season prior (2018-2019) he had 110 points in 81 games and was third behind McDavid and Kucherov. He was a finalist for the Lindsay along with those two and posted a career high in points.
His worst season was in 2017-18 when he scored 76 points in 82 games, that was the first time he wasn't PPG since 2012 and ultimately finished 28th in the league. The two season prior he scored 89 (2016-17) and 106 (2015-16) points and in that year won the Hart, Art Ross etc. The seasons prior to that he was winning cups.
So, I guess you could argue 2017-18 was an "uninspired season" finishing 28th in the league in points but every other year since 2015 when the Hawks last won the cup he was top 10 in the league. I would not say that was several uninspired seasons. I think people just forgot how good he was.
To recap, after the 2015 cup, Kane finished 1st, 2nd, 28th, 3rd, 8th and now sits 2nd in points. He is second in the league in points in that period with 499 trailing McDavid by 10 points. He is second in goals scored after Ovechkin and third in points per game to McDavid and Kucherov.