The Luftwaffe was decimated by the 8th, 9th and 15th AF fighters in 1944-5; that is a fact. 
 In the 18 months or so the P-51 was in action the Luftwaffe in fact inflicted far less losses than the 840 stated; many of these P-51 losses were to flak and ground fire while strafing; see for example the 355th Fighter Group record as evidence (although they also include P-47 losses the principle is proven)- 365 air claims, 505 ground kills, for 191 aircraft lost, of which just 46 losses were due to Luftwaffe fighters, and 83 to flak (and the balance due to non-combat causes) 
 But if you have access to more verifiable figures for kill claims and losses then by all means please share them with us- otherwise the numbers here have to remain (which derive from several sources including the definitive 'The Mighty Eighth' tome.)