Ok so if I've understood you correctly - the big thing with EV's is that they have nowhere near the drivetrain loss?
All energy conversions (eg chemical to heat, heat to mechanical, mechanical to electrical, electrical to light, etc) involve losses. Some things are hugely inefficient, others are the opposite.
Electric motor efficiency is around 90%.
Really big diesel engines used for power generation achieve 46 - 48% efficiency in practice depending on operating conditions. That's taking into account losses in the engine (most of it) and alternator (minor).
That's for the largest internal combustion engines in use for fixed (not ships etc) power generation in Australia - they're 17.5 MW each. That's not large compared to steam or hydro turbines but it's as big as it gets for internal combustion.
Now the reason for mentioning great big engines like that is they're as good as it gets. Once you make the engine physically smaller and/or lighter relative to its power output, that comes at the expense of efficiency. Smaller and lighter but less efficient.
Then there's the problem that every time you hit the brakes, that energy is lost and in practical driving that's significant. Versus an EV that can recover not all but the majority of that via regenerative braking. Tricks like that aren't breaking any laws of physics but done well enough and they can create a situation where the real world fuel consumption of the vehicle "seems like" the engine is impossibly efficient (eg the Mercedes 50% efficiency). It's all above board, just akin to treating a saving as though it were income basically.
Idling whilst stopped in traffic is also a dead loss with internal combustion but no such issue with an EV.
To put some figures on it, take 1 litre of diesel fuel, run that through a great big engine in a power station and use the electricity to charge an EV. It'll move you about 25 km so about 4 litres / 100 km.
Of itself that's not hugely impressive but:
1. Very little electricity is actually generated from diesel or other oil-based fuels. For Australia as a whole it's about 2%. Non-oil sources have advantages in terms of supply security and so on quite separate from any environmental considerations.
2. Even if the source of electricity does involve burning fuel, exhaust emissions aren't normally discharged at ground level into a densely populated area in the way that conventional cars do. Rather, the power station's a considerable distance away and has a great big tall stack. Some impact on urban air quality possibly but far less.
3. To the extent the world's going to use renewable or nuclear energy sources, they produce electricity they don't produce petrol. Whilst not impossible, it's also a lot harder to get petrol out of coal than it is to turn it into electricity.
End result is an EV doesn't use zero oil but it uses stuff all compared to any petrol or diesel car.