Heavies do tend to have the worst Aim of the bunch, but for me at least they hit enough over the long run for me to be satisfied. Once you get some perks setup for their rockets those can be incredibly useful and game changing if you use them at the right time too, especially if you run with 2+ Heavy soldiers like I started to at the end of that Classic game when I was having trouble keeping my veterans alive. I started giving them Archangel armor so that they could be up above the battlefield raining death with both their plasmas and rockets/blaster bombs. Since height gives you a better chance to hit it balanced out in the end.
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