The Prius Prime does Toyota’s complex, but also kind of simple Power Split Device transaxle. And the latest Prius engine is over 40% efficient.
I think one of the issues with the steady-state-genset methodology is on-demand power and charge/discharge efficiency. Yes the generator/motor is efficient either way, but charging energy into a battery pack and getting it back out has a bunch of loss. The next issue is hard driving - If the genset is designed only to run at optimal efficiency, you’re probably looking at something like 20 horsepower (a guess based on optimal Prius engine range). If your driver is on the freeway driving a bit aggressive, or doing other not-recommended activities like towing (you should see what has been towed by a Prius…), that could be continually exceeded until the pack was depleted. With Prius Prime, when in Hybrid mode, the engine responds to demand and then takes a % off the top for charging - generally, depending on battery state of charge and current power demand level. If the pack’s low enough it won’t add any electric boost, it will only take take take… a bit higher and it will allow net 0 charging for the highest power demands, but still not give any charge up… and higher yet it will allow some electric boost to the drivetrain.
There’s been some other very interesting points about the viability of home charging for EVs/plug-in hybrids. Super valid! Not everywhere is suburbs. Yes, this model works very well for traditional American suburban living, but fails most elsewhere. Rural electricity grids may not be up to handling a fast charger at every location - and the same goes for stressed, dense urban grids. Even more for urban locations, is Space and Charger Access (as has been mentioned already in this thread). Almost everyone in a condo or apartment will not have charger access. The last time I went to some EV company’s website (I’m not even sure if it was Tesla or another), they had a survey that included questions about if you owned your home and if you had a garage (and detached/attached) to try to determine if EVs were “right” for you, in addition to other questions about daily miles driven.
A last point: I see a lot of arguments online about cost of ownership and cost of entry for EVs, but I rarely actually see “home charger installation” mentioned. If I fully drain the range on my hypothetical Tesla, how do I charge that overnight if I don’t have some kind of fast charger installed? A standard outlet/circuit in US residential is 120VAC*/15A, so 1800W. Wouldn’t the “base” of ~65kWh for a model S take 36 hours to charge that way? Okay, so you install a second Dryer outlet… pay the electrician… you get 240/30. That’s still a nine hour charge, and I’m assuming there’s no charging losses here. Or let’s say the 54kWh pack, current lowest for a model 3 (at least that I saw on Wikipedia). Still 30 hours for 120/15 and a work-night possible 7.5 for 240/30.