yes, that's in general a good idea, but it doesn't answer the question.
in the article https://de.airbnb.com/help/article/3421 is written "There are different kinds of discounts and promotions available, but only one offer can be applied per stay."
Actually I can't retrace this fact for the custom promotion combined with last minute discounts.
But the last minute prices are not combined with longer stay discounts, what I would like to use actually.
The behavior of the combination of discounts seems a little bit inconsistent.
I think, the most comfortable would be, if airbnb provides a flexible configuration for the combination of the discounts, that every host has the choice, how the behavior of the discounts is to eachother. The least would be, that the better discount for the guest is used auomatically, but it doesn't seem like that, currently.
best regards
Carsten