The battery is really pretty small compared to a 'pure' EV. Capacity is stated at 6.5kWh but in practice, we will likely only get to use the 'middle' 60% of that most of the time. It probably won't charge past 80% of actual capacity as that kills the cells if you do it very often, same for the bottom 20% - its best avoided for battery longevity, so the system will be reluctant to allow use of it. To help preserve battery life, MB are going to program it carefully. If we got 4kWh I'd say that was a fair guesstimate. If you look at the charge times, they tend to bear out that guess. I confess I haven't studied it carefully, but I think ours is recharging from 'empty' to 'full' in about 2 hours or so on an 8A charge. That's 4kWh or so. I'll take a closer look from now on and see what it looks like. From there, figure in how much power heating (LOTS) and A/C (fair amount) uses, lights less so as they are LED so pretty efficient, systems loads then finally the actual driving along the road. Again, less efficient than a pure EV as we have that 7G-Tronic Plus to power.
All things considered, I'm pretty impressed with how well ours is doing so far on pure EV range.
It's like the quoted mpg figures for any car - take the published numbers with a large pinch of salt until you have been able to either try it yourself or at least gather some real world results from the community at large. A hybrid like this is going to be massively sensitive to how you drive and the nature of your journeys.
If you are lucky enough to do a large chunk of your driving within the EV range then you are going to be very pleased with the economy. If you pound up and down the motorway, you probably won't. It's also going to be sensitive to terrain - rolling along the flat is low demand, up hills is going to be challenging on the battery and you never get back all you put in, although it does feel pretty good to know that braking or coasting downhill is putting something back in the 'tank'.
As we've seen, some folk are getting low 30s, some are getting over 130. PPM might be more worthwhile a value given the dual-source of power though.
JP350e's numbers look like a goal to aim for to me. Massively different to those numbers suggests there might be an issue. Whether that is a fault in the car or driving technique is another question though

I'm looking forward to trying out the performance a bit. That'll nail the range.