One might wonder why didn't Hilliary figure out how to use Facebook. The answer might be, that she did, but just like with the Russia buying their own ads with peanuts money compared to the DNC spend - it didn't really matter. Seeing people parrot the Russia narrative, the same day the Man himself testified that it didn't actually happen, entertains me a bit.
Anyway, you are completely right about how overused the Russia line is without data on its interference effectiveness.
So... That did happen.
With sanctions freezing huge amount of their assets the Russians didn't really have any serious plays against the US except pushing the soft-power propaganda angle[1]. Essentially they (Russians) just kept trying lots of random things[1], in high volume, until something stuck -- and it worked, spectacularly well too, mostly due to decades of propaganda already shaping the Republican base.
Hilary was marketing hard on all platforms, but some estimates put the Russian spend at $400k USD per month, on top of NRA, GOP, and other heavy Right-Wing spends.
[1] see RAND Corp research about this: https://www.rand.org/pubs/perspectives/PE198.html