Ideas and suggestions.

Regarding Eagle Eye, the only reasonable solution is to allow a hero with the skill to see and use in battle the spells that are in the opponent's spellbook (without percentages). Artifacts should provide a bonus instead of percentages, based on the level of Eagle Eye. For example, having an expert level of Eagle Eye allows you to see and use all of the opponent's spells from level 1 to 4 in battle, and having another artifact that provides a bonus to the skill allows you to use spells up to level 5. Without the Eagle Eye skill, but with three artifacts, you can also see spells from levels 1-4. This would counter starting mages with level 4 spells, but Eagle Eye wouldn't be overpowered; it would allow you to use the skill and artifacts at least sometimes, and add more variety to the game.