Races in Heroes 5.

Strictly speaking, 5% isn't a significant number. At level 21, it's just +1 to a single stat. It's easily compensated for by any skill boost, an artifact that boosts knowledge, or (even more so) education. The real question is whether you should rely heavily on druid magic; it's nice and all, but it's not entirely equivalent to pure magic.

This is just an example of what usually happens on average; sometimes, random chance can produce completely different results, as it did for me with Jezebel in a scenario. At level 16, or perhaps higher, she only had 3 knowledge points, which is very strange for a demon, even compared to necromancers, warlocks, and knights, who usually have at least that much by this point. However, her magic skill was 5, and it was growing faster than her knowledge.