This may well apply to some merit sources, but certainly doesn't apply to them all. Merit sources don't really get that much per month to distribute when compared to the amount of posts being made site wide, and especially when merit sources are encouraged to send higher amounts per individual post than users who only have sMerit they've "earned" to send.

Merit sources don't get an unlimited amount of sMerit to send, and I think a few might dip into their earned sMerit from time to time. Remember, that the merit that merit sources get allocated to distribute refreshes periodically. It is certainly plausible for a merit source who was selected because they are good at identifying good posts to find a good post per day. That's 30 sMerit if you merited every single post with 1 merit alone, but this is hardly the case, and several often reward more per post.