I agree, there's no reason to think large haul electric trucks will have a better efficiency margin over internal combustion variants than in the case of passenger vehicles. On the contrary, there's reasons to doubt it, for example large diesel engines are highly optimized for efficiency unlike small consumer cars they are bought by businesses which think in TCO.
So probably the real margin over diesel is about 50% cheaper in fueling. But you have to take into account route restrictions due to limited range, time lost charging etc. Not to say it won't find its place in the market, but the margin and advantages of electrics are not yet so clear cut, it will take decades to reach dominance.
You are only taking into account the negatives and ignore the positives. Electric trucks will have cheaper maintenance. TCO is much better in pretty much all electric vehicle and every study looking at vans in cities has shown this. Semis will most likely show the same thing.
Such semis will also be faster exhilarating and more maneuverable and be a much more pleasant vehicle to drive. All those things are worth something as well.
Of course they will not dominate from day 1 simply because can't produce enough but they will eat away at ICE market share every year for a long time.
By the time they can produce enough of them to take on long haul routes, batteries will be 2-3 generation further along and the economics will tell.
Also the maintenance TCO at scale. A large fleet operator has a staff of experienced diesel mechanics. Is Tesla planning on making a profit on servicing battery packs for these things?
Battery packs are not designed to be serviced, I would imagine that a Semi has like 4-6 packs and each one has to be fully replaced. The same thing goes for the engine, you just remove the whole engine assembly and put in a new one if one breaks.
So probably the real margin over diesel is about 50% cheaper in fueling. But you have to take into account route restrictions due to limited range, time lost charging etc. Not to say it won't find its place in the market, but the margin and advantages of electrics are not yet so clear cut, it will take decades to reach dominance.