Which units would you replace in the Sylvan castle?

You could choose not to remove magic, but in that case, the Elves would have as many as 3 spellcasters, and any Academy would be envious. And the spells would be chosen wisely. For example, against Dungeon, the Fairy would always choose "Fist," and the Dragon would never use "Chain Lightning" if the enemy has only one stack of units, and wouldn't waste "Ice Ring" on a small unit. Then the Elves wouldn't be a weak race, that's for sure.