In short, I prefer a rule that hands out the discount "early" rather than one where the discount only appears where downtime is plentiful.
That is, if and when the campaign features a long stretch of downtime, the issue at the oppoiste end of the spectrum - the crafter running out of money - that is the lesser problem.
Why? Because that's not a problem - even when you're out of money, you can still Earn Income just like the others!
What this means is that the discount doesn't only appear at the whims of the particular campaign. As long as there is a week of downtime here and there, that's enough for the crafter to gain the listed benefit.
Since this benefit (roughly 20% off, give or take) already applies (just obscured), it isn't unbalanced. Just clearer and more upfront.
(Based on CaptainMorgan's summary of Age of Ashes, a character does benefit from crafting in practice. He concluded a mid to high character could make thousands of gp, which very roughly corresponds to 20% off of an item appropriate at that level)