As an aside, I don’t think any of us outside of CoG have the data to make that claim. I’ve seen people try to cobble together estimates of my XoR earnings based on download ranges shared by Google Play and Steam; those estimates are consistently way off. The sense that HGs sell more than CoGs seems to me to be more based on online buzz, leading to people being surprised by what’s on the actual top 20 sales lists and e.g. shock that a beloved, much-memed and discussed HG series like the Infinity Saga isn’t up there.
If the average HG (or even the average successful HG, clearing out the unprofitable outliers) was consistently earning more than the average CoG, I’m pretty sure CoG would tweak the guidance for writers accordingly. In the past, they’ve not hesitated to adjust it when Robots (and, on a much smaller scale, Rebels) showed new paths to sales success. My small window on the company doesn’t suggest that they’re unconcerned with profit; they put out their guidelines because they think those lead to more successful games than turkeys. And nothing I’ve seen from the outside suggests they’re way off on that judgment.
Of course I wish CoG shared their figures with us so we could all second-guess their business strategy more effectively. 
But for some reason I doubt that’s going to happen.