Re: "Did the Russian intervention actually swing the final outcome ?"
The possibility that the Russian dirty tricks affected the election outcome is relevant because some fraction of the unhappy Democrats never will think otherwise, despite the fact that its probability is vanishingly small and impossible to determine anyhow. The claim will continue to be made at least through the lifetime of people born before 1995 or so.
It certainly is worth doing something about it, but indicting Russia-based GRU officers and employees seems a pretty anemic something indeed. Unfortunately, beyond strengthening computer network defenses and educating voters (who constitute a vast sea of deep political ignorance and apathy) and campaign and election phishing targets, nothing else is likely to have much effect. Educating voters is, for the most part, a lost cause, since it would require a significant uncompensated effort on their part and most of them are uninterested or they would have learned much of it in secondary school history and civics classes. Hardening the computers, networks, and users is well known to anyone in IT security to be a hard problem in which a single misstep can bring disaster.