He doesn't have that explosiveness as he did in Orlando, and he doesn't have finese to compensate that lost brutal power. PnR finisher, and defense core, would be his best role, but obviously that's not the dominant role. He doesn't want to be that kind of second banana to Kobe, there is no way he wants to sacrifice for Harden.
Unless Rockets figure out a way to have Howard coming out more, it's going to be a long season.