Diesel hybrid, better or worse mpg?

Theres lots of discussions and reasons of why Toyota doesnt make a hybrid diesel, but im curious to know if one were to exist, do you think it would be superior to their atkinsons counter part?

Maybe a small car like a prius will not benefit as much, but a highlander hybrid or sienna hybrid might have a lot of potential.

A diesel engine running at low rpms all the time, which is its peak energy efficiency curve. The only difference I would change is not having it turn off and on while driving unless stopped longer than 4 seconds and batteries are mostly full. I know having the engine running continuously mitigates the fuel savings, but at the same, a regular diesel vs a hybrid diesel, a hybrid diesel can have the advantage of running low rpm and having the electricity it produces do all the work of acceleration while the engine just acts as a coasting maintainer and generator. It would be superior in that sense to a regular diesel.

Now vs an atkinsons, large cars that are hybrid dont gain that much mpg vs their non hybrid version. Toyota is the better of the hybrids because the max theyll put in their big cars is a 2.5L engine. While as their competitor like GM put a 6L atkinsons in their hybrid version of the tahoe, yukon, escalade. Only to gain an increase of like 4mpg while driving in city to a whopping 20mpg. Pathetic. Id imagine a hybrid diesel tahoe would get a solid 30-35mpg or more IF it existed. The diesel version by itself already gets 28mpg on the highway and 21mpg in the city.

It isnt like diesel hybrids dont exist, theres a very slim few in europe and most notably is the Mercedes e300 diesel electric. Their diesel hybrid gets more than their gas, at 37.7 - 57.7 mpg. Their hybrid gas engine 22.8 - 39.8 mpg. Does this not prove diesel is more efficient to be paired with a hybrid transmission in some cases? Or at least, all diesels would be more efficient if made into hybrid diesels.

And of course, when an engine is running all the time as a generator, it would make sense to have the battery capacity double or triple of a normal hybrid. That way the extra electricity created while the engine was idling makes up for it not turning off and on as much as say a prius would.

 

While thats very neat indeed, i dont think the cost to produce electricity from fuel compared to charging at home or running straight gas is economical otherwise id do it myself too.

It says the tesla semi gets 1.7miles per kwh. The most efficient generator i searched up is .166 gal per kwh. Firman H08051. Thats 10 miles per gallon which is pretty good for a semi actually. Normally they get 6.5 per gal.

Can someone make sure my math checks out, because whats stopping people from running diesel generators and converting cars into hybrid EVs without the need for massive batteries.