The point of acquiring Granlund isn't to have him when you're contending. It's to trade him for value as a rental next year (as in 2024-2025) when he's a pending UFA.
With Simek, you're getting no value because he's a fringe NHL defenseman making decent money. With Granlund, you're paying more but you also have the chance at getting positive value back for him.
And that's what the Sharks will get when they trade Granlund as a rental.
Granlund for Simek adds $2.75 million for the Sharks next year while it gives them an actual NHL player. The year after, Granlund will be a rental and will be very easily tradeable for value.