I'll admit I don't know much, and fewer facts.
Having said that logic tells me a transmission is large & heavy. The moving parts cause friction which decreases efficiency.
At some point electric motors and batteries will reach the point where they are more efficient.
Of course the other wrinkle is refuelling. Hard to beat the ease / speed of gas or diesel. That too will be over come.
Case in point mine trucks that are pure electric https://electrek.co/2017/09/17/electric-dumper-truck-worlds-largest-ev-battery-pack/
Or, diesel / electric locomotives.
