Actually, the regeneration works quite well. In a car with a charge indicator, you can see the battery charge significantly with moderate braking at typical city cruising speeds.
The batteries can't absorb all the energy, due to the mechanical, electrical, and chemical losses. But, it's enough to provide at least some of the subsequent acceleration.
A smaller displacement, but high output turbo engine that would give you all the on-demand power for acceleration, lugging and towing. It would revert to a preset "best efficiency" RPM once cruising speed was attained.
This is what hybrids do -- they are programmed to run the engine at best efficiency and either supply needed torque from the electric motor, or channel excess engine power into the generator to charge the battery.
And some of them have high-output turbo engines that are smaller than would be needed without the hybrid systems. The BMW i8 has one, although it's certainly an expensive model.
Four motor/generators, one at each wheel to provide, all wheel drive, electric braking, and traction control.
I don't know if any car has four motors, but there are several with three: a single drive motor/generator on the engine transaxle, and one on each of the remaining wheels.
In the case of the Acura RLX Hybrid, the real wheels are differentially driven or retarded with positive or negative torque, and assist in turning the car at lower speeds.
The AWD Tesla's have one motor/generator for each pair of wheels.
I realize you are actually referring to a fully electric system that decouples the engine from the drivetrain, like a diesel-electric locomotive. The early models of the Chevrolet Volt operated like that most of the time. But, it still had a mode that would clutch into the drivetrain in certain circumstances. And, the 2016 Volt eliminated that in favor of a new system that acts like most hybrid systems: when the engine is running, it provides some torque to the drivetrain.
Perhaps an engineer can explain exactly why no one has gone to a pure electric drivetrain. I suspect it has something to do with delivering maximum horsepower to the wheels when the battery is depleted -- there will be a significant loss in the electrical system without the direct coupling.
And due to that loss, highway cruising will require more power than if the engine is providing it direct to the transaxle, resulting in lower gas mileage.
You may be seeing "surface charge" which is different from having been trickle charged or constantly charged over a longer time period (like a road trip).
Like you said, storage cells can't instantly accept all that charge, or you could pull into a charging station and then leave in a few minutes...just like a fill-up.
Another concept I've been daydreaming about is the "battery."
Actually I use terms "battery" and "storage "cells" or "EV cells" because in automotive nomenclature a "battery" generally refers to a package of EV-cells wired in series to provide the desired voltage and ampere hours.
My concept there (and it may already be in use, or under development) is to build a "battery" which is a combination of EV-cells (for durable charge) and a bunch of Megacapacitors (for instant charging) and probably some diodes to control current flow.
None of that is rocket science, and I'm surprised I haven't seen the idea being being talked about. It seems like regenerative braking, or a quick "fill-up" would then be possible.
You sound like you like the individual hub-motor/generator with just a power-cable running to it (like a brake hose) I think it would make AWD and traction control so simple.
Just like rack and pinion, and struts...think of all the iron it eliminates.