More Numenorean ships did indeed go south, but that number includes King's Men who established colonies at Umbar and points further south. They did not all go to Gondor, far from it.
Arnor was the High Kingdom, it is impossible for me to believe that Elendil didn't have at least as good a library as his sons in Gondor, and let us not forget many books and records must have been lost in the Kinstrife and destruction of Osgiliath.
Aragorn, when asked by the Hobbits where he learned his history tells them 'the Heirs of Elendil do not forget all things past' thus citing his own people's literary tradition as the source of much of his lore. And don't forget the Northern Dunedain also had access to the Elven libraries of Mithlond and Rivendell.
There is in short absolutely no good reason to assume Arnor was behind Gondor in learning and lore. In fact, given Gondor's imperialist preoccupation, the Northern Kingdom may very well have been ahead of her in this respect.
And even the Gondorian sources *are* the only ones it wouldn't make them any less biased. Aranarth and his Men had been resting and recuperating in Lindon for months before the Gondorian forces arrived. Why shouldn't they be fit to take part? BTW the account in the Appedices says troops came from both Lindon *and Arnor*. It's kind of hard to believe that Men of Arnor would have fought in this battle without their new King at their head. Clearly the Gondorian chroniclers just didn't see fit to enlarge on their role, prefering to exagerate the contribution of Gondor instead.
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