If both parties are unified in pursuit of one goal, then we may act vigorously on it over the long term through the course of multiple changes in which party controls what. If both parties can't stand each other enough to cooperate on anything, then foreign policy and behavior will be half-hearted pushes in constantly changing directions.
Russia can't and doesn't want to control us entirely. They do want us to not interfere effectively in their attempts to control the neighboring Eastern European states.
As for the pro-LGBT/liberal ads: One of the strategies the Russians used here was to infiltrate and divide. Only propagandizing to one side of the American political spectrum isn't as effective as playing both sides and turning them against each other.
These ads are just the tip of the iceberg. There were still countless bots and sockpuppet accounts used to sway people one way or the other - but typically against one another.
It's worked really well, and keeps working today.