Ah, this sort of thread is why I love Paradox Forums. Thanks for the post OP
I'm broadly of the view that while marginalism might be a bit more accurate, its probably not a good idea to implement it, as it would create more complexity for little end result.
The period is dominated by shift the means of production. So as factories start to appear, the amount of (for example) clothes that are available increases enormously. Whilst the number of artisans might decrease a bit at the same time, the demand for those artisans services is decreasing much, much faster. The reducing supply of artisans will have a little effect... just not very much compared to the much bigger changes happening.
Trying to model the effect of reducing pop numbers is just one more thing to try to balance in the game... and given the difficulties PDS had in balancing Vic2, I'm keen for them to keep things as simple as possible.
In any case, how they implement the economy is going to be VERY important to the success of the game.