If rumors are to be believed, without reflectors on, the F-35 should have a radar cross section smaller than a quarter (which is a bit larger than a 1 Euro coin). On top of that, its radar is purported to outrange Russian and Chinese radars by almost 2:1. Just looking at it for air supremacy missions, the thing is basically invisible (to radar), and can launch a missile at an enemy jet before they could even detect it, if it wasn't basically invisible.
I mean, even if it had a larger cross section it could probably pick off Russian fighters before those could do anything in return. But with the stealth it has, it could creep up on them and they wouldn't even know what happened until it was too late.
