There's more to it. The use of social media for example by Russians to create false narratives and exploit some voters.
I agree with you that the exact effect on the outcome cannot be quantified. But when one candidate gets several million more votes but the other wins by having won 70,000 particular votes in a narrowly defined set of areas, the possibility cannot be discounted.
Trump does himself no favors in this regard when he pretends like he had some mandate or the largest inaugural in history. The facts keep biting him in the ass on these claims which are so easily demonstrated to be false.
Russian Twitter trolls? Really? Again, I'm not denying anything that they are accused of doing...I'm just skeptical that it actually changed anybody's vote. I don't think many, if any, votes were changed in Wisconsin or Pennsylvania because they read a tweet from a Russian troll account. If what they did consists of social media troll accounts and spearfishing some documents, that's a problem, but honestly it amuses me more than anything, especially internet trolling.
I agree that Trump does not have any sort of mandate based on the election result; he loves to tout the margin of victory in the Electoral College, which is what decides the election, but his victory was actually much narrower than that would indicate, and more people actually voted for Hillary than him. He knows that, and despite his victory I think that bothers him and makes him insecure.
I also agree that Trump loves to do this thing where he doesn't speak about Putin and Russia in the harshest possible terms (like you're "supposed" to do), and it's done absolutely deliberately to drive people crazy and control the news cycle. His actual actions against Russia haven't been so nice, and that's where more attention should be paid.
Again, I'm still not all that impressed by what Mueller has found so far. I'm not dismissing the possibility he finds more, but there isn't anything yet that ties Trump
personally or his campaign to document hacking, Twitter trolls, or any other Russian efforts to influence the election. The best thing they've got is Michael Flynn lying to the FBI about talking with Kislyak. If there's another cockroach lurking somewhere, I bet they get it from Flynn, who is cooperating with Mueller.