There were two artificially created reasons why humanity was so weak. One reason is that Prime Nexus had given the purebloods of the other races their racial aspects, which would continue to enhance and evolve their bloodline as they progressed further on the seeker's path. Which was the most fundamental method of developing oneself as a biological organism, the most superior path of evolution was never a mage or a warrior, but as a bloodline holder.
Second was the world Will; it took humans a very long time to realize that there was something called the Will of the world, which was a completely separate entity compared to Prime Nexus, which was an alien existence. The world Will of the Eldarion continent was actually intentionally suppressing the human race from growing stronger.