We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "dennis@home"
saying something like:

If everything is "otherwise equal" they will perform identically.

The 12V motor needs to deliver the same amps x turns as the 24V motor to
give the same "power".
It has twice the AHr capacity so it is quite able to do so for the same
time.

The 24V one could deliver more amps x turns as the 12V but then it wouldn't
last as long.

Exactly. Just look at the battery size required for a mains drill -
Dinorwig, ffs.