The merit sources don't share the merits amongst themselves in your above senario. The less merits to share around, the harder it is to obtain those merits should equate to higher quality posts to obtain the fewer merits on offer.
Less merits = better, quality posts.
So you want people to grind for every single merit? Even in current situation where there's abundance of merit, forum numbers have been dwindling down for years so I don't think that it's in the forum's best interest to make it even harder to rank up. After all, isn't the main goal of the merit system to make it harder for shitposters to rank up, and not make it a heavy grind for an average member? (imho it shouldn't be)