the victory to loss ratio is not 5:1 for the mustangs of the 364th it is a bit less than half of that.
I really do not think this proves much of anything in favor of either plane. many of the 38 losses were early when 38 pilots found themselves facing a more experienced enemy who was numerically superior. when the mustangs finally did arrive it saw the americans with an advantage in numbers and pilot quality and with the arrival of the mustangs improved escort tactics were also employed.
when you look at the stats, you can see that each unit had a high scoring month or two that gave the decided edge to the mustang. this was later in the war when the luftwaffe was on the decline. so when you consider that with all the advantages that the mustang saw in combat over the 38 it should have more than just doubled the score if it was such a superior aircraft. and doubling the score of the 38s record in the eto isnt a great feat when one consideres just how many planes the 38 shot down in air to air combat.
I think that this isnt a question of 38 vs 51, but a case of proper tactics, better pilot training, leadership, american pilots facing more equal odds, and a decline in luftwaffe pilots.
as far as the second engine being an advantage or disadvantage it seems many pilots abandoned aircraft that may have made it back to base had they stayed with the aircraft. one can only imagine that since they were over land it was safer to take their chances of evasion or capture and bail out vs staying with a plane of unknown flying condition. Pilots in the pacific flying the same aircraft with the same battle damage usually stayed with their aircraft because it was more dangerous to bail out in the pacific than to stick with a damaged aircraft and take your chances. the sharks, japanese, disease, insects, crocs, snakes, head hunters, or just being stranded in a jungle or the middle of the pacific ocean is a lot of incentive to stay with an aircraft as long as its flying. men in the eto and mto atleast stood a chance of evasion and if captured...well I am sure the germans were much safer than what the pilots in the pto faced.