Taylor Hall is not his ideal linemate.
Having them both on the same line is wasting an automatic zone entry and creates uncertainty in transition, along with two weaker defensive minds. They haven't lit it up because they're too similar. More than that, they're spending too much time trying to see the ice the way the other one does, attempting to thread the weirdest passes.
Ultimately with Hall gone, Hughes will likely do better with a Zacha or Boqvist. The latter is also a playmaker but is a bit more conservative and predictable. More than that, he's shown that he's decent at retrieval along the boards. Zacha is best as the receiver of the pass off the zone entry because he's a mediocre distributor in transition but very good with static setups.