IMHO
When trying to minimise hand movements left/right, a long space bar is ideal.
Ergonomics implies that there is little to no hand/palm movement, its all fingers, a good ergonomic keyboard does not require large spacebar or any key to be diferent size, proper key placement is more important than size.
That being said boils down to how big/small your hand is, using same keyboard, someone with smaller hands will "travel" more than someone with large hands, thus a long spacebar is ideal to minimise that, concordantly, someone with extra large hands will have trouble being precise/fast, finger thickness being just one of the factors where distance between the keys is paramount to achieve both.
Back then the only thing you could to on those typerwiters is... write... no playing games, controlling devices, 3d modelling, etc, plus, a decent one wasnt cheap.
I believe we have much better understanding of keyboard ergonomics than 40+ years ago when only a very small category of people would use one.
Standard keyboards are not ergonomic, they are cheap to produce, companies succeeded on convincing most people that the regular shape of a keyboard is normal, just think about the ammount of money being saved by not having bent/flexibile PCBs/connectors