Marner isn't being propped up by anybody, but having a guy like Tavares on your line would boost anyone's production - this was true for his entire career with the Islanders.
It's possible to have a linemate help your production while not being "propped up" by them. Draisaitl helps McDavid's production, but McDavid is far from being "propped up" by him.
I actually don't buy into the idea that Hyman really negatively impact a line's production so long as their are two elite drivers on the line and he's not asked to do too much puck carrying or playmaking. Nylander and Matthews, Marner and Tavares etc. The prevailing theory is that forward pairs are really how you build your top 6, and complement them with a well rounded "third wheel" who can retrieve pucks, crash the net, and hopefully bury as many chances as possible. Some recent examples:
Rantanen & MacKinnon + Landeskog
McDavid & Draisaitl + Chiasson
Matthews & Nylander + Hyman
Ovechkin & Kuzy + Wilson
Kucherov & Point + Johnson
Malkin & Kessel + Hagelin
Crosby & Guentzel + Hornqvist
A guy like Hyman may mor chances off of passes from guys like Marner and Tavares than a true top line finisher, but a lot of the time he's the reason those guys even had the puck in the first place. Usually you hope to have a guy with more skill as that third wheel, but you also don't usually have two players of Marner and Tavares caliber to begin with, so I think it more than evens out. Hyman is also unusually good at retrievals, so that helps as well.
Gaudreau lacks another first line quality play driver to pair with - the numbers show both Monahan and Lindholm are only able to generate offense like a third liner when away from Gaudreau.