I can't argue with people who lose their reason in support of a candidate, but I'll try.
She clearly lied, and Comey confirmed same to Congress.
Comey stated she clearly displayed extreme carelessness with sensitive documents. Look up gross negligence in a legal dictionary and you will find extreme carelessness. He chose the words carefully.
The applicable statute doesn't require more than gross negligence as grounds to prosecute.
For whatever reasons, Comey decided he could not recommend prosecution (which in itself was a stretch beyond his role), but to suggest that he didn't lay out a case for how she violated the statute is just intellectually dishonest.