The battery charging doesn't really create any heat, my laptop stays prity cool unless I'm really utilising the processor, I'm in agreement that charging while using your laptop will add to the heat generated, but 95% of the heat is going to be through the utilization of processor, GPU hard disks etc.
If your laptop is plugged in, it will run faster because its able to draw more power as there is no requirement to preserve battery life, and thus will run way hotter, I can very much notice the difference.