But actually, that's part of TFA's argument.

As spices became less expensive, TFA argues that became popular among poorer people. And so richer people instead came to emphasize the intrinsic flavors of foods.

But for that to work, those foods had to be high quality, and unspoiled. So, by TFA's argument, it was poorer people who came to use spices to mask low quality and spoiled foods.

Depends on the spice and the part of the world you're talking about. Chilli was/is used heavily in Mexico and India to add or mask flavour but, also they also have antibacterial and anti inflammatory properties in countries were you have / have had large concentrations of poor people.

Classical French Haute cuisine is heavily flavoured with fats (butter and creame) which required a lot of milk to create, i.e. the yield is low considering how much precious milk one had to put in. That was something that was at the time exclusively for the wealthy.