In that case, the system should be modified to complicate such merit abuse as much as possible
The easiest way possible I can think of is to reduce the overall amount of merit that merit sources get each month.
I didn't think that I will ever say this, but maybe we reach the point where there's too much merit going around for this amount of quality posts, which then makes it very easy for shitposters like the one mentioned in OP to advance through ranks.