@Greg:
I don't get it.
Why would anyone argue that 'realistic proportions are a necessity for shonen manga'?
If that thought even enters a reader's mind, not only are they looking for entertainment in the wrong series, they're in the wrong genre.
Well, there are also some sites which take everything from a real world physics angle and analyse power levels by doing some totally not overcomplicated computations… which also relies on proportions. That is, if Oda drew let's say Akainu's super nukes only one millimetre longer or shorter, they would get a completely different result regarding how many megatons/gigatons/whatevertons force is involved.
These sites are actually fucking hilarious as for example I once saw them arguing against Master Roshi being able to destroy a moon because it didn't fit their computations and powerscaling and therefore is an outlier which doesn't count at all. Despite well, Master Roshi just doing so...
Reading through that may take its toll by removing a little part of my soul, but it's funny so who cares...