Aha! Someone else that uses this method.
This is the map I use all the time, setting the circles to ~100 miles. Makes sense because if the circle from the supercharger you're at overlaps with another supercharger circle then you can likely get from one to the other. If they don't, then you probably can't.
Now the Tesla-style map (200-ish mile bubbles) works if your destination is inside a bubble and has charging AND your next stop (supercharger or destination) is inside the bubble of your current stop. But that definitely takes more planning.
The 100-mile bubble map is pretty much the map to use if you just want to be able to safely drive on superchargers alone.
With that in mind, there is a lot of area completely impossible to cover on superchargers alone. Whole states still, like Arkansas and North Dakota have zero coverage on this map... even most of Maine, Mississippi, etc. A few states have near-100% coverage like Florida, California, New Jersey, Ohio, Delaware, Massachusetts, New York, etc etc...