To say that Cam Newton (and baseball players) have punching power because they can throw a ball, means you either have no idea what you're talking about or you're just forming dishonest arguments. I think it's both though, first and foremost you though Anthony Joshua was 6'3" to begin with, then when you found out he was 6'6" 250 you came up with even more ridiculous stipulations, you're simply judging athleticism on who runs faster and nothing else because Cam is faster, but will quickly discount power for Joshua by saying Newton has it too because he can throw a ball

Meanwhile Joshua's power is a lot more easy to see, since he's taking peoples' heads off.
I'll address the punching power question because you're so adamant. The other stuff in your post was just my mistaking Joshua's height, which I corrected, and so doesn't matter. Alternatively, Cam being the same size and faster doesn't *just* mean he's faster. As I explained previously, faster guys are generally better at everything related to athletics than slower guys. It's all correlated.
Moving on, boxing power utilizes the same basic mechanics as throwing a football, so Cam should be able to punch hard:
"You engage up to about 50% of your mass throwing a shot like your hook. Again, your technique plays a big role in how much mass is involved in your power punch.
The way the body mechanics works is by recruiting a chain of various body movements to transfer momentum (energy) to your point of contact. You generate movement from the legs, the torso, arms and whatever component of the body that generates momentum as part of the motion in your technique. All the energy from those components combines and transfers by kinetically linking all the momentum to the opponent. You’ll get a good component of momentum generated from the legs initially, but a large bulk of the mass comes from your torso as you pivot it in an angular trajectory (twisting motion). Recall that Force = mass * acceleration. Elite fighters like Pacman have an average punching velocity of around 12 meters/second, so what’s left is the mass, which usually depends on your body type and the technique to optimize it. Guys you mentioned like rumble have a larger upper body mass, which when rotated about the axis of the spine, generates a lot of power."
^
This is similar to the process of how a NFL QB throws a good football. He generates movement in his legs and torso, before uncorking the ball in a kinetic whipping motion, which is initially calculated by Force = mass*acceleration, but QBs can add more force through technique (same as boxers).