"Half the efficiency" is highly optimistic. Afaik making synfuels loses about 70% of the energy and then you burn the stuff in an engine that is at best 40% efficient. Meanwhile EVs have >70% wind turbine to wheel motion efficiency.
Imagine saving all of that for a much smaller battery (say, 100 miles range) which is enough for 45+ weeks of the year, and then for the rare case of driving further than that you bring gasoline with you, with its vastly superior energy density and thus range. Only for those few trips. It can well be super expensive, but who cares, it's only for that rare trip to the grandparents or the skiing resort. And then you don't need to care much about the bad end-to-end efficiency. After all, you don't care about that when taking a plane to Hawaii either, do you?
Currently, plug-in hybrids tend to just be used as gasoline cars because people are lazy and don't charge every night. There are gas stations everywhere, fuel is cheap, and you are used to filling up gas anyway. But once gasoline prices spike to 3x-5x because it's synthetic fuels, the dynamic will change, fewer gas stations around, the reduced economies of scale lead to further price hikes and boom, everybody will use their plug-ins mainly as EVs. Which is what I'm describing above. Which could outperform pure EVs because you don't need a 500 miles EV range anymore, you can make do with 100 miles.
Or build public transit for the commute and don't use a car at all.
I understand the drivetrain argument. What about a simple generator to recharge the battery on the go? Like the original BMW i3 had. That one didn't take off, but likely in part because it was ugly, too small to be practical, and the gas prices still being very low.