Except that you need to compare against the Cricket $60 unlimited deal that offers tethering and throttles it at 6GB. Even then they aren't quite on par since you don't have the 10 free data sim cards, free international data, and ability to make and receive calls from any device that has hangouts installed.
Google Fi is also flexible in that you don't have to spend $80 a month if you are using less. When I don't have to do a bunch of tethering for work, I usually spend $30 - $40 a month total.
Thus Google Fi cheaper for a variety of use cases. Different plans/carriers are cheaper for different use cases. Just because a carrier other than Google Fi is cheaper for your use case doesn't make Google Fi outrageously expensive.
If they're literally charging double compared to the domestic competition, it's pretty outrageous.