“The article also says it significantly reduces mpg.”
Energy of E85 is about 4% lower than non-ethanol and about 1% llower than E10 but ethanol has a higher octane offsetting loss a little.
Most drivers will not notice a difference from the E10 presently blended.
“...ethanol has a higher octane offsetting loss a little.”
I suspect the gasoline refined to be mixed with ethanol will have its native octane reduced to the point where the add of ethanol will bring it up to the pump sticker promise.