His gathering of information is diligent in comparison to that of those covering the matter at established news organizations. "Obsessive" may be a more appropriate term. "Delusional" is a term that would be more appropriately used to describe a person's conclusions/beliefs. He's not a "Russia expert", and neither are most of the journalists actively covering this subject. I think it's important to distinguish between the roles of "Russia expert" and "expert on the Russia investigation" or on any of the specific subjects the election touches on. You obviously need Russia experts to put understand what's going on, but you also need people who're experts on the specific focuses of the investigation, to the extent that's possible. I'm not saying Abramson is such an expert mind you.