Is a Left Punch harder than a Right Punch?

[Jimanuel Boogustus]

It can't be quantified like that. Each fighter is different, whether each punch is thrown with the same quality technique matters and on and on and on.

I agree.

It would also depend on the physique of the boxer, how his muscle mass is distributed etc.

A long-limed boxer with enormous lats and shoulders, with the right technique would probably have a bigger straight rear-hand.
Whereas a boxer with thick set legs and over-sized biceps and chest would probably favour a hook or uppercut.