Actually, nobody knows the answer to these questions. Fighter pilots of all nations overclaimed kills anywhere from 2x to 5x their actual kills over the course of the war, depending on tactical circumstances and the conventions of the air arm or unit, as verified postwar from the loss records of the other side. This was all known to each side's brass at the time, but big kill numbers and lots of aces are good for morale, so they quietly used much lower and more reliable estimates for their own planning.
Your sources for "2x" and "5x" are?Loss records for the Allies are far more complete than Axis records, german records seemed better than IJN until 1944 when both went 'south'The majority of aces, who claimed 5, 6, or 7 kills, actually never got 5.
That is a bold statement and sounds like a claimed 'fact' - If an opinion, everyone has one of those. If you think it is factual what are your proof points to both qualify and quantify that ANY percentage of aces with awards of 5-7 in fact had less than 5?The total numbers and the kill ratios claimed for aircraft like the Hellcat are

.
What is your claim for total number - that you pose is 'not BS'?
5, 50, 500, 5000? and what sources would you cite to support your conjecture?
what approach do you suggest to bring it down to 'hard facts' or extremely high probability of 'fact'??Although overclaiming was universal, it occurred more at some times and places than at others, and therefore we cannot reliabily compare not only the absolute, but even the relative numbers of kills credited to different aircraft in different theatres.
AgreedHeavy bomber gunners often claimed around 10x the number of aircraft that the enemy actually lost, which is Glyn's point. No kill tallies for B-17s or B-24s, individually or collectively, can be taken seriously.
Also agreedOne could do systematic analysis to get the real data, making heavy use of the records of the side whose aircraft were shot down, except that (1) there would be major gaps in the data, (2) the question isn't of enough importance to interest any real historian, and (3) the pseudo historians who dominate the WWII-aviation-history genre are much too interested in perpetuating the old myths to be interested in the project.
Major disagreement on 2.) unless you have a unique qualifier to the definition of 'real historian'. The air war in Europe is a very concentrated body of perpetual study - with more seeking Truth than "proof' August