you would be surprised... he still carries the same weight as other MW's so the mass behind the punch will be almost the same (he could actually have more due to overnight weight gain) but with his long levers at range he will possibly generate more power. Also do not confuse length of muscle as having no muscle with longer limbs his muscles will be longer and thinner but of similar mass. Depends on how is shoulders and back are shaped also as they can generate massive torque in punches ala Tommy Hearns.
In my personal experience any really tall bean ball I have seen fight carry no power. He's not going to have same power in his legs or shoulders to generate the power of a normal size middleweight.
In my experience they do ! As i said there isnt really that much less muscle on them, there biggest weakness by far is in short range inside fighting where their long levers are less effective and fail to generate power in shorter punches however on the outside they can often generate more power due. Longer levers generate more power, its physics....
If I think of all the people I know who can punch really hard most are stocky with short arms, less distance between power generated in shoulder to the end of the fist. Someone at 11"6 st and 6'7 is spread to think and won't be able to cope with big punches.
In terms of generating power the further a distance to be travelled thro the lever means there is more time for acceleration to increase the speed, in turn meaning the mass is travelling at a higher velocity, which increases the force. This not opinion but fact. This is obviously only accounting for long levers v short levers. There are other factors to consider obviously such as technique, shoulders etc but in terms of long arms v short arms you cannot dispute basic physic laws