British historians aside, there is a crucial difference between Moscovy and Novgorod: Moscovy was a country on its way to become a nation, primarily focused on eating the rest of the Russian principalities. It was interested in territorial expansion above everything else. Meanwhile, like you said, Novgorod was pretty much an oligarchy where the powerful merchants held all the influence, but unlike Moscovy, they were not interested in nation building, or territorial expansion, they were interested in money (and as long as trading was working the rest of the world, including the rest of Russia, could burn for all they cared). So sure Novgorod was not some liberal or really republican country, but it was very different to Moscovy in its core.