Both the Druid and the Sorcerer have WITS as their key attributes, but it doesn't seem to affect the casting of spells or their effect in any way. Is this true?

Magic is talent based in this game, not skill based. The game is skill based though and it is through skill use you will get Will Points. To have Wits as the Key Attribute for Druid and Sorcerer is logical based on the character and "typical" skills for those professions.

Both the Druid and the Sorcerer have WITS as their key attributes, but it doesn't seem to affect the casting of spells or their effect in any way. Is this true?

I would say that WITS is the most fitting for the magic-based archetype based on *other* things they are expected to do in the game. It is however not in anyway needed to better cast magic. Some things affected by WITS:

- Ability to resist magic (with Insight)
- Ability to handle fear-based attacks (which almost all monsters do)
- General knowledge about stuff (lore)
- Sharp senses (scouting)

You are definitely free to create a magic-based character that doesn't follow these archetypes, which I see as a strength of the character creation in Forbidden Lands!