The drivers should get a fixed percentage of what the customer pays, whatever the customer pays. We don't really know what the correct charge would be, but t he number quoted to the customer and the one quoted to the driver should be the same, and it is claimed that it isn't.
Let's say Uber's cut is 25%, they quote $10 to the driver, but they charge the customer $15. If the correct amount is $10 then the driver should get $7.50 and Uber $2.50. If the correct amount is $15, then the driver should get $11.25 and Uber should get $3.75. If they are scamming as suggested, the driver gets $7.50 and Uber gets $7.50, which is either twice or three times as much as they should get.