I would love to have that guy up on the stand to explain the difference between "shall" and "may". That he's Obama's man doesn't change the law.
IANAL and again I'm looking for the transcripts but going by memory his thoughts followed these basic premises (which I'm probably summarizing badly if not outright incorrectly):
1. The whistleblower may have been someone not in the intelligence community or related to intelligence activities, therefore the statute didn't apply,
2. The DNI sought advice by the DNI Legal Counsel, and their opinion once rendered is nominally binding
3. The POTUS still has a fundamental right to redact portions of even whistleblower reports due to executive privilege and other claims.
Again, these aren't my arguments so don't beat up on me for repeating them (or trying to repeat them to the best of my recollection).