You need to win games in the regular season to make the playoffs, which we didn't do this year, and Couture certainly helps this team do that less than Gaudreau would.
And then you need to win playoff games after earning that berth to win a Stanley Cup
Gaudreau isn't young anymore, we've seen a body of work and it's not pretty when the postseason rolls around
His PPG drops from .959 to .615 from the regular season to the playoffs (.633 if you count the qualifier games), while Couture's actually jumps from .764 to .87
His teams have never been past the 2nd round, have only been past the 1st round once and have only won 8 of the 26 playoff games they've played with him (11 of 30 if you count the qualifier games)
And these weren't scrub teams, he played on the division winner with a Norris Trophy winning teammate just last year and Gaudreau went from scoring 99 points in the regular season to getting just one secondary assist while his team was bounced in 5 games
On top of that, it's not clear just how much better Gaudreau is in the regular season than Couture right now
In the 2020 season Gaudreau scored 58 points in 70 games for a pace of .829 or 67 points in an 82 game season
In the 2020 season Couture scored 39 points in 52 games for a pace of .75 or 61 points in an 82 game season (or 48 points had the season finished and Couture played in all 64 possible games accounting for his time missed)
All this while battling injuries and playing on a far inferior team
Give me the player who paced for 6 less points but plays center, plays better defense, and is the far superior playoff performer, that's Logan Couture
Couture is aging and has a questionable contract, but Gaudreau isn't young anymore, he's 27, and he's about to get a nightmare contract of his own in the 2022 offseason
I don't have a problem with the idea of adding Gaudreau to the Sharks, but I do have a problem with it being at the cost of Logan Couture