You can watch the video of the tests drive done by a journalist in normal traffic conditions. With a large pack size you run the engine at peak efficiency only to charge the pack and then shut it down. The pack does all the peaks and valleys of demand. This is how diesel locomotive work and they are the most efficient land vehicles exactly because of the electric drive train. Diesel locomotives just don’t have a pack for the regenerative braking or peak shedding. Some do now and it doubles those locomotives fuel efficiency.
Here is a link to the actual video of the drive. I leased a Prius for 6 months it would do 90 mpg over ten mile runs in gridlock and 75+ mpg in typical suburban and urban use over 20 mile trips. So it’s not a stretch to see 100+ with a dedicated genset running at its peak efficiency point. They did drain the pack to zero first so it’s all genset to pack to wheels.
Yes, dedicated ICE to charge batteries, with the electric motors used for propulsion, is very efficient.
Be nice to know how efficient the ICE powerplant is. If it is above 40% efficiency, it may be above the efficiency of central electric generation + grid losses.