Sorry but that formula doesn't work as you have portrayed it.
The AH3 uses it's brakes like any other F30, so only a small percentage of that braking regen is actually harvested.
The biggest problem in 'harvesting' brake energy is the randomness of situations, and the human factor. There is no AI good enough to predict what you as a driver are intending to do. It would help if the car had a thumb operated regen brake, so you could use that instead of the brake pedal.
No doubt the AH with go into harvest mode when the throttle pedal is at 0%. If you were driving correctly, anticipating traffic conditions ahead, you would use this mode to coast. In the AH it would be like applying the brakes softly, which means you can't coast as far.
You talk about weight of the batteries, but the system also has extra rotational drag, add all these negatives up and you soon realise you are going in the opposite direction to efficient motoring physics.
Lastly, if you have managed to drive like a nun and re-coup some of your capital outlay, the first invertor failure you have will soon have you back in a big deficit. Invertors are notoriously fragile.