Almost - In production models the engine does act like a series hybrid generator under most circumstances. At high speeds, the engine was directly connected to the drive train as it is more efficient to do that. the transaxle of the Voltec system is a marvel of engineering. It supports a dynamic switching between series and parallel hybrid mode as well as using the two separate electric motors for either power delivery or can switch one to regen and can rapidly switch between those modes, too.

That remains true for more recent "series hybrids" as well, such as the Honda mentioned in the article. The efficiency gain from engaging the ICE when cruising on the highway is just too good to pass up.

Exactly. The Volt uses the same planetary gear set style transmission that the Prius does.

Everyone bemoaning the death of the Volt can now just buy a Prius Prime (the PHEV variant). It's the same thing just newer/better. It even looks sporty-ish now.

It wasn’t my suggestion, but what I read way back in the day, and it may not be accurate but it does not violate the laws of physics. It’s entirely possible that (just as one hypothetical example) being able to keep the engine at optimal RPMs at all times in a series hybrid creates more efficiency even after the extra conversion losses.