You don't have to buy any "narratives". It may be better to simply take stock of the chain of events of what actually happened.
In this case - was there, in fact, something like a high-level, coordinated effort on their part to conduct various covert social media shenanigans (as opposed to open campaigns, like buying ads) in the U.S., for whatever purpose? Maybe the effort was ultimately futile and wasteful (like the "Illegals Program" a few years back -- but the more important question - was there such an effort?
Available evidence increasingly indicates that, in fact, there was.
How much was spent on these adds, how many hundreds of millions? Oh just $100k.
No idea where you're pulling those numbers from. But the overall scope easily suggest a budget >> $100k.
Did the Chinese buy ads, the French?
Wide-scale social media trolling != "buying ads".
Without hypotheticals, here is Qatar giving a $1M birthday "gift" to Bill Clinton