And even a typical mid-war Spitfire was pretty impotent against everything apart from a Zero
I believe this, along with the previous couple of posts, are most relevant.
It wasn’t a matter of what you were shooting
from - it was what you were shooting
at. In the Pacific War the vast majority of targets were unarmoured and the extant machine guns were more than adequate for the task and it would not have been logistically efficient to build another logistics chain and aircraft models for the European theatre.