Like about 50lbs, he's got a decent chin, good perseverance and pressure. With that being said as is he was running off fumes before the halfway point.
He was never a devastating puncher even when he was on peds. What he had going for him was relentless pressure, mixing up his shots, getting good leverage and snap on the inside with his enormous size, and clubbing guys against the ropes once they were inevitably backed up. There was absolutely none of that in the Dubois fight. He was basically a tank with very limited ammunition and couldn't even hurt the shaky chinned Dubois after the 5th or so because he was out of gas. The more winded you are, the more difficult it can be to really throw with sharpness. That spelled disaster for Miller since his only slightly above average power fizzled out to below average and he could only throw arm punches or attempt one big desperate haymaker every 40 seconds. Blocking with his face didn't help either and since he was so goddamn heavy, it was relatively easy for Dubois to use lateral movement and light him up with jabs basically every round. Miller is probably done at the elite level (and to be honest, his ceiling was never very high to begin with). His only slim chance of a comeback is to lose at least 40 lbs, bring up his cardio, work on his defense, and establish a jab. Probably too late now and he'll likely end up a gatekeeper/journeyman if he doesn't retire. Wouldn't mind him fighting Ruiz, Joyce, or the other big baby Anderson, those could he entertaining scraps.