You're right that it isn't about the volume because there is no causal relationship between breathing rate and nitrogen loading. And if that's true (which it is), the diver who is is breathing slow and light will NOT incur less decompression penalty than the diver who is breathing heavily unless the difference in breathing rate is caused by differences in physical exertion.
And has been pointed out by others already, shallow breathing leads to poorer CO2 ventilation, increasing the risk of hypercapnia. I don't think you should advocate potentially harmful practices.[/QUOTE
Go back and read my post. I said similar work rate, the diver with a greater oxygen efficiency who is breathing slow and light because of a more effective oxygen transfer rate will incur less decompress penalty than an out of breath diver breathing heavily and there are large benefits for a diver who takes the time to improve their fitness and breathing technique.