I believe I have seen this quote and "reign of evil" is not the same thing as eternal winter.
We're talking about a place where magic actually factually raises the sun and moon. That is sufficiently different enough on its own to throw out any resemblances to Earth universe physics as isolated coincidences.
We can take nothing for certain or extrapolate on any sort of physics basis as the science (talking about the fundamental idea here) of Equestria is different.
Sufficiently different that we should take nothing for granted as a starting point, not merely the same unless shown.
EDIT: Yes we have
"era of evil" not reign, but nothing about say the implications of no-sun=no-heat.