"other cities" is the indefinite plural. "the other cities" is the definite plural.
Since, theoretically, we can list "the other cities" (in the example at
hand), i.e., at least somebody knows which cities they are, i.e., can
'define' them, make them 'definite', "the"
seems to be the theoretically correct choice.
On the other hand, presenting "other cities" as indefinite, i.e.,
"whichever cities they may be (provided we include all of them)" seems
equally logical to me.
So I, too, am hard pressed to see how the choice of whether to present
the "others" in this sort of comparison as if they are known or as if
they are unknown amounts to a choice of formal or informal.
CJ