'The rear-wheel drive cars will be able to go zero to 60 in less than 4 seconds. '
I don't believe that.
I don't believe that.
Not really. There are multiple Ford and Suburau models (off the top of my head) that will run sub-6.0, some models $10k cheaper than the Model 3.
Of course, where most people judge a car's power while driving it normally is the 60-80 mph time. That's the only time most people floor the accelerator, when they're pulling out to pass someone. Gasoline vehicles have a marked advantage in this metric.
One of the motors is turned off when not needed so you can run essentially half-power and yet still have the second one available in a split second.
For EVs you're largely just fighting against Ohm's law(constant voltage requires that you draw more amps which means resistance generates heat, etc) and to a lesser degree weight. Which has much less impact like you note.
My basic understanding of ICEs is that they are most efficient when you can run them at a specific RPM(and tune for that RPM) which is why you see Diesel-Electric Locomotives where the ICE largely acts as a generator.
That's spot on. This is why you can't use the cam from a generator on a car and vice versa (even if it is otherwise the exact same engine, such as with the Willy's engine). The cam on a generator will be very pointy to open and close the valves across a very sharply defined moment in the engine cycle, whereas on the car version the cam is much more smooth giving a wider operating range (but at lower efficiency).
The reason why Diesel Electric locomotives use the electric motor to drive the wheels rather than using the diesel directly is twofold, one the efficiency that you already noted, the second reason is that the electric motor does not need a clutch and has a torque curve much better suited to getting a large weight accelerated (much like steam power is better than ICE's at this, it's the exact same reason).
It sounds like less than 6 seconds is what we should expect from the base model though.