Pages 86-87 of the following RAND report https://www.rand.org/content/dam/rand/pubs/rgs_dissertations/RGSD147/RGSD147.chap6.pdf quote a 9.1:1 loss-exchange ratio between USAAF and Luftwaffe single-engine fighters to June 1944, a
It’s not comparing like with like at all.
Against total LW fighter losses in Europe, the figure it gives for US losses seems to be (a) only fighters, not bombers and (b) only for the 8th AAF. The Germans were usually busy trying to shoot down bombers. If you add in losses of B-17s and B-24s with 10 or so crew a time you get a different picture; also if you add in the non-trivial losses suffered by 15th AAF. The RAF may have made some small contribution too.
Not to say that the LW wasn’t being overwhelmed and wiped from the sky. But that 9:1 ratio is misleading.