I think to some extent whats being suggested is that, in a pre Warcraft 3 Northrend human colonists wouldn't have to deal with TOO many threats. Who knows what sort of relationship they had with Drakkari, it might have been peaceful it might have been minor skirmishes. This could also explain why so many Northrend native races were willing to become "mercenary" to Arthas in Warcraft 3. Iron dwarf stuff, not an issue. The Taunka, their nomadic tendencies could go either way. The blue dragon flight likely largely ignored the humans and certainly the Nerubians were content to remain hidden below. Vrykul remained slumbering and potentially did the Gargoyles. Tuskar are also rather accepting of these "strange" creatures from the south, as if this wasn't new to them.

So from a human nation stand point... yeah... the important parts of Northrend were likely "human territory" just as I'm sure they would argue many other parts of Lordaeron were despite the presence of other civilizations/sentient species. They would have had little urge to go to the colder more dangerous places like Icecrown, which was likely greeted with "It's cold... and icey... why bother. Stormpeaks likely has a similar issue. I'm sure some went up there but maybe never returned. Sticking to the more climatized environments (even including Dragon Blight in that) would be not only more hospitable but also more profitable for resources like food, fur, mining and even limited agriculture, which we see in Wintergard. Obviously Wintergard isn't a major city (assuming it existed before hand) but it would have been to the locals. I mean... weren't there tombs for nobility and what not obviously they would have been there before the war effort.