Rishadan Dockhand is one of several homages in Modern Horizons 2 to powerful older cards that are powerful enough on their own to bring the flavor of the older card into Modern.
The obvious comparison here is to Rishadan Port, a Legacy staple that has given aggressive decks an easy way to disrupt their opponents early turns enough to win the game. It is typically played alongside Aether Vial, a card that lets you stop caring about your own lands and use them for disrupting your opponent. While this combo was more typically used in the Goblins archetype in Legacy, we now have a powerful way to try it in Merfolk in Modern.
Merfolk has had some scattered success in Modern, but one of the weaknesses of the deck is its 1-drop slot. There are an abundance of 2-mana lords, but not many merfolk with relevant text that cost a single mana. Cursecatcher can be decent in some matchups and irrelevant in others, with some lists choosing not to even run it. But Rishadan Dockhand gives us a larger body and a way to disrupt our opponents that could be just enough disruption to buy the time needed to build a board of fish and close out the game.