I don't think you can take out a single player from that top line and say the other two wouldn't have missed a beat.
That line had amazing synergy together. Take out Hudler, and yes, Gaudreau suffers a little bit. Take out Gaudreau, and Hudler suffers a bit. Take out Monahan, and yes, the other two suffer.
Nothing wrong with that. That is called synergy.
I would like to add that any line that Gaudreau was put on worked fairly well offensively. Conversely, any line Hudler was on also worked nicely. They both make players they play with better with their vision and puck skills. No idea why people are arguing Hudler vs Gaudreau in terms of who helped out whom - they BOTH helped each other out incredibly.