The myth is that Pentagon wouldn't admit to it even if their life depended on it. The Su-35s have engaged the F-15s over the Southern Syrian area of At-Tanf. The only ISIS pocket closest to Damascus, 250km distance. The american air force has been covering this area in particular, as when Syrian Military destroys this ISIS pocket. Then Syria will have full control over its entire Jordanian-Iraqi border, all the up till Abu Kamal, where River Euphrates cuts through the Syrian Iraqi border.
The Su-35s won these engagements, successfully forcing the F-15s to back off. In one instance the one in the pair of Su-35 locked on the F-15, trailing for a good part of a minute. It was only due to descelatory hotline set-up between the americans and Russians, did the two disengage.
The only myth is the americans still barking about their superiority over everyone else. The only advantage usaf has over RuAF, is numerical. Where are far more F-15s than there Su-35s. Russian Aerospace Forces are more concentrate with modernized and deadly fighters, rather than bulked out with a old junk. As time goes on, Su-35 production will ramp up. At present RuAF has less than 100 Su-35s. In time the numbers will rise to meet adequate numerical strength.