I'd point out as well that Hayward's rebound, steal, block, and assist rate are all pretty much in line with his career averages, or better.
The biggest differences are his shooting percentages, usage rate, and free throw rate.
He's not SO far off his career averages of 47.7% from two and 36.5% from three.
In terms of his shooting percentages, the one real glaring issues is that his last season in Utah he shot almost 70% within 3 feet of the basket, and those shots made up almost a quarter of his attempts.
So far this year, those inside attempts are down to a fifth of his shots, and he's hitting only 53.6% of them, which is quite poor for a player of his size.
But he's a career 63% finisher within 3 feet. If he can regain some of that interior finishing, while pushing his shooting percentages closer to his career averages, that will probably go hand in hand with improved confidence taking more shots and attacking the basket a bit.
Hayward attempted 16.5 field goals per 36 his last season in Utah, consisting of 5.4 threes and 11.2 twos. He also attempted 6.1 free throws per 36.
That usage rate of 27.6% is probably higher than he'll ever get in Boston. But if he could get back to something like 14 field goal attempts per 36, while getting to his career averages in shooting and free throw rate, his box score line would look something like this:
16.1 pts - 6.2 reb - 4 ast on 43.5 / 36.5 / 82.2 shooting in 32 mpg.
I imagine some folks might still complain about that kind of production on a max contract, but if he has some big games in the playoffs, I suspect even those complaints would die down.