Peak ability and peak season aren't necessarily the same though. There are many things than can go right or wrong within a season that leads to varying totals for players that aren't always indicative of their ability. From that idea I think there needs to be sense that a player's totals are reflective of his play and repeatable to put full stock in them. Sakic was obviously a great player, but that season stands out among his others, in both offensive totals as well as GF% (where Forsberg usually had a significant advantage) to the point where I think it's both a combination of him reaching a height of his play, but also a year where everything goes right. Forsberg in general was a slightly better player while they were on the same team imo, and from 02-03 to his foot injury after the lockout reached a peak level of his play that was higher than Sakic's, but unlike Sakic, didn't manage to have a season where everything goes right. So I would consider him a better player in that period, and if I had him healthy for a tournament, I would take him over Sakic, but if I was looking to get the most value over 82 games, I would take Sakic's '01. It really just depends on how you want to frame it.
It's the same with Crosby, who doesn't have a year as good as Sakic's '01 either, but who is pretty unanimously considered to have the better peak. Or even say Kane, whose '16 season was at least as good offensively relative to league/peer scoring as Crosby or McDavid's best years, but I don't think anyone would argue has as good an offensive peak.