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.
I don't really think this would actually help because majority of these merits were not distributed by merit source and so it doesn't really solve the problem.
The number of merits distributed by merit source monthly continues to drop, if you check the DdmrDdmr merit dashboard which is a clear fact that most merit source don't even use much of their allocated Merits because of low quality post and issues like this.
While some of these Merit source may actually just store them others in the WO, just spend it on those who they know won't abuse there and it's quite annoying when I see post about criticism about how spent their sMerits where as most of the merit sources there are still actively distributing merit across each boards to quality posts.