This "cells in parallel" fixation is a red herring. There is no substantiative difference between having a two-metre long electrode folded up in one cell and two one-metre long electrodes in two cells connected in parallel: the electrical conditions on each square centimeter (or whatever) of electrode are identical.
There may be some slight differences due to the separate electrolyte, but the electrolyte in these batteries is largely immobilised in the porous separator anyway.