Backlash is too harsh
It seems unbalanced that rolling a ‘1’ when casting magic causes Backlash. If the player then fails a Spirit check, they takes 1d10 damage, which ignores armor. Most powers don’t do that much damage. Roll a ‘1’ while casting Mage Sight, fail your Spirit check, and you’ve dropped Hellfire on yourself. Congrats!
Backlash is the primary balancing element for powers. There is no limit (spell slots, spell points, etc.) on how much a caster can use their powers. Using magic as an example, anytime a character opens themselves to the aether there is a risk represented by being Shaken (minor consequence) on a failure or backlash (major consequence) on a Critical Failure.
Secondly, unless you roll Critical Failure on your Spirit check, you have a good chance of being able to use Fate to avoid the backlash. As a result, a mage with Elementalism d6 only has a 2.8% of being unable to avoid the backlash. Yes, if you roll two Critical Failures in a row using magic, something bad happens. If a caster thinks twice about using their powers frivilously, backlash has done it's job.
Magical attack powers do more damage because they add the caster's Spirit, usually to a d10. Elemental Strike is Spirit +d10 plus the elemental effect for example. Even if a mage suffers backlash the average roll on a d10 is 5.5. So, with a Toughness d4, their passive is a 3 and they take 2 Wounds. The real damage lies in a max, but the odds of that are only 10%, when combined with the odds of two Critical Failures the net likelihood of that occurring is 0.2%.
Scribe of the Adventure System