That's still many orders of magnitude too little. We're currently talking data rates on the order of (optimistically) 5 Mbit/s for a cell with a diameter of 15

That's still many orders of magnitude too little. We're currently talking data rates on the order of (optimistically) 5 Mbit/s for a cell with a diameter of 15 square miles, i.e. something like 0.1 Mbit/s per km^2. In very rural areas (which is the use case!), that's infinitely better than nothing, but anywhere people live, this is effectively nothing, and there is currently no way around ground-based infrastructure.