Rapid shots will never do the same damga as unload.
From my lvl 17 Powertech :
Rapid Shot : 108-149
Unload : 175-204 per second
It means that during 3s, 2 Rapid Shots will deal 216-298 while unload will deal 525-612. At this you add the fact that Rapid Shots have 10% less accuracy...
If you still believe unload is a waste then...
The damage difference diminishes a little at level 50, with my current gear its 2100 damage with Rapid Shots vs 3200 with Unload. Rapid Shots is still the best to use in most cases as you can stay mobile. Only when you are stuck at range for some reason and have no reason to move away from or closer to your target should you use unload.
Due to the channel time and heat, it's a free attack. Used in conjunction with TSO, you can actually attack AND vent heat with Unload. Next time just be quiet and let the adults talk.
Sorry to correct you on this but you should never
use TSO with Unload. At long range use it with Death From Above. At close range if you can afford not to move use it with Flamethrower. Both abilities do superior damage to Unload, cost more heat that you save, and have the same 3 second channel time that lets you vent heat.