as a recently fervent convert to the amazingness that is Battletech and Mechwarrior, I will say that some mechs just have SHITTY heat control no matter what you do. part of that explains why I prefer Autocannons. they generate a LOT less heat than energy weapons and Missiles.
The solution is to use kinetic weapons instead of energy ones. Back in mechwarrior vengeance, used to just go for the gauss cannon and a few machine guns. It did the trick!
It's true, one thing I did back in Mechwarrior 2 was put so many heavy lasers on the mech and grouping all of them as one, I didn't even survive a frame after shooting