Size is overrated. Wilder at 210lbs could knock Miller out and that's just 20/25lbs north of what Beterbiev weighs in the ring.
20-25lbs is a pretty big difference in combat sports. Wilder is also 6'7 and that right hand is far, far harder than anything Beterbiev is throwing.
Not with his style. A man can't give up over 100lb and fight in the phone booth with a dude that does that as his bread and butter.