You are right in one measure, thankfully, intelligence and justice are institutional efforts. However, it is highly likely to be interpreted as obstruction of justice if it is demonstrated Trump believed removing Comey would put a stop to or impede the investigation of Flynn, especially considering the handling of the Flynn investigation was held close to the top of the FBI due to the sensitivity. This has been explained by people with more legal qualification than myself. A jury or what-not may disagree with this but from everything I understand this is definitely a fair game in many lawyers' eyes if Mueller find something more concrete than Comey's allegations on what Trump said.