And you missed the point entirely...
The point is not that Garland is a more efficient scorer/line driver at ES than random winger. The point is that this matters less than a player's overall contribution to a team. You could get more out of Pettersson, more on special teams play, that would make up the difference in losing Garland's ES superiority.
But they'll have Lindholm to do this, no? This is why they re-sign him for $7m+. If they felt that the Garland solution was enough, then they don't re-sign Lindholm, imo.
If Garland could mesh with Pettersson, things would be a lot easier.
The RNH example is one of a player who is worse at ES, while providing a net conversion benefit to other skilled linemates. A skilled player working with other skilled players.