i think all classes as it stands are perfectly balanced, and they all have their strengths and weaknesses against other classes, the argument about the heavy and the scout, yes, up close the scout will have a decent chance of winning, but if the heavy can nail the scout with a shot or two at range and it's good night Vienna.
i think the pyro is reasonably well balanced, contrary to popular belief, it's short range, so engage at long range, if ones coming toward you then back peddle,anything but a heavy will be able to out pace a pyro long enough to kill them, and a heavy will win in a shoot out, it's a very difficult class to get good with, but it's rewarding when you do (even if everyone is complaining about your skill

).
a few tips for not becoming KFC is to avoid engaging them in a corridor, if you see one coming toward you just steadily back off and keeping aiming shots at him, he will drop. the worst thing you can do when faced with a pyro is to act like a headless chicken, i have seen this so often when i enter a room/control point thats being camped by the enemy and they will go into a mad panic, shooting wild, and i'll be able to torch half the room before they can drop me, same goes for the scout