Of course it does.
Those 4p cards cost you 8 Provisions during deckbuilding, and you need to have them in the deck (not in hand, milled, discarded or otherwise disabled) for the combo to work.
This "11 for 5" argument is so fundamentally wrong that it isn't even worth any more time. It makes literally no sense when you look at it from a logical perspective.
I agree that a simple "11 for 5" is not true, however you cannot deny that you have to run 4p fillers in any case.
All cards will cost 4p in the deckbuilder, so for a 25 card deck it makes more sense to consider the 50 + leader provisions upgrade provisions you invest to upgrade those initial 25 4p cards and in this frame you quickly see that provision-wise you invest only a single provision to upgrade into this combo.
The fact that the Mage Assassin has to be in the deck is admittedly a downside, however it being thinned without any additional cost about makes up for the opportunity cost of having to run it.
I disagree that those 2 4p cards cost you 8 provisions, given that these spots have to be filled by 2 cards, which costs at the very least 8 provisions, even if you would not run the Mage Assassins.
Also compared to the other thinning packages Blightmaker + Mage Assassin costs 1 provision less and gives 3 points more, while not having to meet a condition on the field (although one can only start the combo with 1 of the 2 cards this also means one can run this package twice).