The best way I found to defeat Fedor on Legend is to use Fedor and just come out swinging.
The guides here call for a controlled attack because they want to ensure a victory and wear down his stamina. It works, but you have to be very efficient. Thus getting frustrated and quitting.
Here's the game plan. As soon as he starts running at you, just throw hooks, as you start to do this, he will too. It might not work the very first time, but keep at it and you will catch him mid swing with a perfect counter punch.
Again, Just trade punches with him, if he starts hitting you in bunches, just back up regain composure and try again, look for his punching motion and try to counter with short jabs, then as you get your timing down, start uppercuts and hooks. It will work sooner than later. and you won't have wasted 17 minutes in one match just to try it all over again.
Rooster Teeth video explaining my nonsense