I've also been surprised that Brown isn't getting more minutes, so I agree with you there.
I'm not sure I'd agree that Brown is clearly ahead of Hayward now.
Over the last two months (Feb and March), the minutes per game are almost the same - Hayward has 25 mpg, and Brown 25.5.
Hayward is shooting 39.1% from 3, 53% from the floor, good for 11.6 points per game. 4 boards, 3.5 assists.
Over the same period, Brown has scored a little more, at 13.6 per game, but he's also taking more shots and shooting a lower percentage - 36% from 3, 48% overall. Brown has the same rebound total, but he's definitely less effective as a creator/ballhandler, with only 1 assist per game.
Brown is clearly the better individual defender, but I'd say he makes fewer headshaking mistakes in team defense/blown assignments.
Net, pretty close, different skillsets.