1) Rafale will not be entering dogfight with its full external load. Fuel tanks will be dropped, and all but wingtip missiles expended, prior to the merge. Empty hardpoints and wingtip missiles cause relatively minor drag penalty, one that cannot negate F-35s far higher baseline drag.
2) Performance penalty due to external carriage is only really relevant when baseline performance is the same, but Rafale has far better baseline performance than the F-35:
2.1) Rafale’s wing loading at combat takeoff weight is 325 kg/m2, which is less than the F-35s wing loading at combat weight (428 kg/m2). Difference is 32%. At combat weight, Rafale has wing loading of 275 kg/m2 (difference 56%).
2.2) Rafale’s canards add 3,6 m2 to wing’s own 45,7 m2. Further, they can be expected to improve maximum lift coefficient of wing by cca 9%. This results in effective wing area of 53,4 m2 and wing loading of 235,6 kg/m2. F-35s horizontal tail adds 11,8 m2 to wing’s own 42,7 m2, but does not make any further contribution. This results in effective wing area of 54,5 m2 and wing loading of 335,2 kg/m2. That is still a 42% difference. Further, Rafale’s wing trailling edge control surfaces have the same effect as the F-35s tail during sustained turn, but at less drag due to cleaner aft lines.
2.3) In order to initiate a turn, F-35’s tail momentarily provides download before settling into a lift-producing position. Rafale’s canards momentarily provide upload before settling into a neutral position in which they create no lift by themselves, but improve wing lift and reduce drag. This also reduces need for Rafale’s elevons to provide download in order to initiate a turn, further improving instantaneous turn rate. Taking a look at the point above, this means that effective wing loading during instantaneous turn is 235,6 kg/m2 for Rafale and 591,3 kg/m2 for F-35 (151% difference), while effective wing loading for sustained turn is 252,7 kg/m2 for Rafale and 335,2 kg/m2 for the F-35 (33% difference).
2.4) Rafale’s canards create an area of low pressure on forward part of the wing. This moves center of lift forward, increasing instability beyond the static instability already built into the aircraft. Further, unlike the static instability, dynamic instability does not shift to stability in supersonic flight. This results in significant subsonic, and especially supersonic, maneuvering advantage even before lower wing loading, higher thrust-to-weight ratio and tailless delta’s traditional planform advantages in supersonic maneuver (no interference drag, large amount of lift) are accounted for.
2.5) Rafale, thanks to its combination of 48*-swept wing and LERX, has an effective wing sweep of 56*. F-35 has physical wing sweep of 35* and an effective wing sweep of either 39* or 55*, depending on how you count it.
2.6) Rafale also does not have internal bomb bays or overemphasis on radar LO, both of which cause a large penalty in the F-35s baseline drag.
2.7) Rafale has thrust-to-weight ratio of 1,01 at combat takeoff and 1,2 at combat weight, compared to the F-35s 0,87 at combat takeoff and 1,07 at combat weight. Combined with advantages noted in previous points (2.4-2.6), this results in significantly better acceleration and sustained turn capability.
2.8) Rafale’s canards not only improve pitch onset and turn onset rates (2.2-2.4) but they also energize outer portion of the wing, thus improving roll onset rates. Combined, this gives Rafale a transient performance significantly superior to that of the F-35.
3) Both external fuel tanks and most missiles are expended prior to the fight. Rafale in dogfighting configuration only has 2 wingtip IR missiles, and contrary to opinions of some people, properly integrated wingtip missiles (here I am discussing the F-16/Rafale/Gripen configuration) actually reduce drag when carried. F-35 on the other hand can either limit itself with internal carriage (which means that pilot has to wait for cca 1 second for doors to open) or carry wingtip missiles (which are carried not on tips of wings but on classical underwing hardpoints some distance away from wing tips, and thus do cause drag penalty). In addition to wingtip stations, Rafale also has two semi-conformal stations on body near the wing root; thus both the F-35 and Rafale carry 4 missiles in low-drag configuration, and both can carry a maximum of 10 missiles.
4) Rafale can achieve Mach 1,8 and cruise at Mach 1,2-1,4 with 6 missiles. F-35 can achieve Mach 1,6 and cruise at Mach 0,95 with 4 internal missiles. This makes it quite clear that the F-35 has inferior acceleration (and thus lift-to-drag and thrust-to-drag ratios) compared to Rafale, even when both aircraft are in air-to-air configuration. Similarly, clean F-35 achieves only 17% greater combat radius than the air-to-air configured Rafale (1.082 vs 925 km), despite having 17% greater fuel fraction (0,369 vs 0,316 at combat takeoff weight) and 75% greater total internal fuel capacity (8.280 kg vs 4.720 kg).