Are some muscles important in a boxing match, some say leg muscles help with power but Fury and Wilder have proved that`s not true as both have thin legs but good power, are any other muscles important? defined abdominal muscles help with punch technique in terms of fluid movement.
Stamina is the key, and that begins with cardio, which translates directly to the leg muscles. No legs you end up like Wilder did.
Rear delts, lats... Every boxer (even at the lower weights) has huge lats. Lower back, core and legs are important too, as they're vital to the punching motion. I started aggressively training my lats & rear delts last year upon discovering this in another thread and have noticed that I hit a lot harder.
Whilst it's not an exact science I would say that having big lats is a good thing if you want to punch hard.
Those help you bring punches back in after they have been thrown, so are important in that aspect, but both are classic "pulling" muscles that won't affect the force of a punch. The "push" muscles in the upper body along with core and legs/hips are what generate heavy force. But yea, rear delta and last are important to boxers. I love neutral grip pull ups for late and facepulls for rear delta.