That is true in cannabis world. But in other breeding however. If a breeder says that his pregnant Angus Cattle will give birth to angus cattle and he's pre-selling the yet to born calves, I expect that I would be receiving Angus cattle and not Jersey, Hereford or Galloway. Nothing wrong with these breeds but I I'm paying for Angus. Same thing with plants, If the breeder say he's selling Blue corn, I expect to receive Blue corn and not Waxy, Flint, or the Dent varieties.
The reason why I'm buying feminized seeds because I want to produce said CBD Blueberry not to breed them or hunt for phenotype. You're absolutely right, that if I want to breed then the route to go is regular seeds, not feminized. Therefore, I expect that feminized seeds are true to the selfied mother (aka stable genetics).
I'm not looking to breed or create my own, I'm looking to 'produce' what they are supposedly selling for consumption and not for reproduction. Otherwise, I'll chuck my own pollen just like everybody else.