Stats don't tell the whole story.
If Celts are so good with Hayward then why is the Celtic record just 16-10 when Hayward is playing?
This may get mis-interpreted by some as blaming Smart, but ... well, unfortunately there have been several games where we played Smart and Hayward together a lot due to injuries to Jaylen and/or Kemba. And unfortunately, the effect up above gets neutralized somewhat when Hayward plays with Smart because Smart handles the ball a lot. In fact, with Smart on the floor with Hayward, the team plays somewhat worse on offense.
Kemba, Jaylen & Jayson all defer to Gordon a ton for playmaking. But with Smart, Brad has him handle the ball because he is less effective as a 'space-maker' without the ball. Teams like the Bucks notoriously sag way off of Marcus unless he has the ball. So this forces Hayward into the corner as a spot-up shooter and negates much of his play-making.
Just watching this current game right now against MEM, with Jaylen out, and Smart moved up to the starting lineup, we see the same effect. The starters struggled to generate offense out of the gate. What little they did was off Hayward (4 assists already before the end of the 1st) but the ball spending too much time in other people's hands.
This team needs to be healthy and with everyone in their proper role.
Important - please don't take this post as a knock against Smart. I love Marcus and he's super valuable to this team. But he and Gordon don't mix optimally on offense. I like Smart best when he's the playmaker for the bench.