I'm no expert, but actually, grade for grade, the A.H. Fox is the better American gun.
JMHO.
And this old Fox(y) agrees 100%. The Model 21 possibly started our in 1931 (or, 1941 if you read Steve Bodio's book on shotguns closely) as a utility grade boxlock double gun, retailing at I believe, $59.95 for the double triggered and manual extractors field gun. Design began back around 1925-1926 at WRA-- interesting to me, as an amateur metallurgist-same time frame when WRA offered their FUBARed stainless steel barrels- (A good friend and fellow WRA buff has a M12 Trap gun and a M54 in .257R, both with stainless steel barrels- when that fiasco ended in about 1930, WRA went to Winchester Proof Steel (AISI 4140)and dropped the Nickel steel alloy for their barrels, receivers, etc--
So, thanks to John Olin's love of the side-by-side gun (see Houchin's book on LC Smith shotguns, you will see pictures of his 12 Specialty grade with extra barrel set- AE and HOT- cased)--and the then new WPS, he allegedly pushed for production of this "work-horse" double, as Parker, AH Fox, Ithaca and LC Smith were seeing their retail sales plummet as a result of the Great Depression.
I think, and this is just my guess, that had it NOT been for the Winchester Custom shop and their made-to-order options to the buyers with "deep pockets"; ie: You could only buy an "off the rack" Model 12, Model 54 or later Model 70- no Super Grades or Pigeon Grades, the M21 might have stayed as the "plain Jane" boxlock-- but as WRA offered options and Custom shop made to order M21's, that changed.
I do not own, nor plan to, either a graded AH Fox or a M21-- I stay with lower graded pre-1913 12 gauge LC Smiths due to "supply and demand" and also, because like Field grade Model 12's, I seem to shoot them fairly well- on game birds and barn pigeons- I am NOT a clays shooter--
I have one AH Fox- a 20 gauge Sterlingworth with 28" barrels, ejectors and DT-- it weighs 6 lbs. even-- a hunting pal has a pre-WW2 mfg. 20 gauge M21 Trap grade- 28" barrels, ejectors, DT and smallish beavertail forearm- and it weighs 7 lbs 3 oz. I rest my case--