it's not baseless, it is an educated guess. Do I have WotC's numbers, no, but that does not mean it doesn't have a probability of > 95%
For an estimate of WotC gets per book, see
Estimating D&D’s Revenue | Alphastream
"If the above model were true for D&D, a product like the $59.95
Bigby’s might look as follows:
- $60 retail price, which is what your FLGS charges you.
- $30 is what the retail store paid to the distributor.
- $15 is what the distributor paid to the gaming company.
- $15 is what the gaming company gets for all of its work. This must cover salaries, printing, art, editing, marketing, etc."
They easily make more profit per book on DDB