I felt the exact same about Brayko. He was my first boss battle after Saudi Arabia, so you can only imagine the despair. A good tactic I found to avoid Brayko when he's coked up, is to run around the middle of the arena, where the speakers are stored. Keep watching which direction he's going in since he does change direction quite frequently and when he's panting, turn up behind him and use CQC on him like crazy. When he's using his guns and guards keep popping in, use traps against the doors to greet them. And then go for Brayko himself, otherwise, if you don't make sure you've taken down his guards, then they'll deal a bit of damage whilst you're running away from him wielding the knife (was a victim of the stray shots killing me). I was also going to advise you use chainshot (a reward for upping your pistol ability) but it seems like you don't have it, unfortunately. Good luck.