To win a U.S. election you don't need millions of votes. You need tens of thousands of votes in strategic locations. It was something like 50,000 votes in three states in 2016 that determined the outcome of the election. Clinton had roughly 3 million more votes but they weren't in the right places. An influence campaign doesn't have to "exerts more influence than the entire media and PR industry put together". It has to move a few tens of thousands of votes in the right places. Also, it's easier to win any game by cheating. U.S. actors are less free to cheat since they will be subject to U.S. law if they are caught. If scales are balanced with 200 metric tons in each pan, you can through off the balance by chucking a hammer in one pan of the scale.

Besides, it seems like the U.S. intelligence agencies are better positioned than random people on Hacker News to assess the extent and influence of the Russian influence campaign. What do they say?