Let’s think about this. All VFR flights fly below FL180. Most IFR flights fly above it. Since this site doesn’t track VFR flights, which altitude do you think you’re going to see more of? Seems to make a big difference to me.
I was trying to bring out that VFR flights are not a factor in the equation.
**You were the one to bring up VFR flights in your initial response. ** Please re-read your original response.
VFR flights do not change the ration of IFR above or below FL180. Yes, you will see more high altitude routes because there are more heavies then pistons in the full scheme of the IFR system.