I think they abstracted the problem so away that they have no idea what they are talking about. Having a single file that contains all your plans and make both your app, marketing pages, and Stripe work from it is trivial and is just good engineering. It's not a "Pricing Engine" or a "Pricing Stack".
There are definitely easier and harder ways to handle pricing, but especially when you have higher touch sales “just use Stripe” stops working in a lot of cases.
Ultimately bespoke sales deals show up, and you need to be diligent in your tooling and pricing design to make it work well (especially if you have any form of metering or dynamic pricing you want to take effect “immediately”)
It’s easy to have the handful of price points and fixed billing. But there’s a lot of ways for things to get more complicated.