This does seem like a very US-centric problem. None of the recipes I was brought up on base their quantities on third party packaging, and generally don't use premixed ingredients. It's very strange.
Some of the casseroles constructed that way from those days were legit delicious but I haven’t seen or heard of them since the prior millennium. I’m not even sure if some of the prefab ingredients are still available. I’d eat some of those again in a heartbeat. You don’t see it on the coasts anymore but the tradition still seems to exist in flyover areas.
NB: I just googled some of these things and the recipes appear to exist online, I just don’t know where to buy some of the canned ingredients.
Then I realized that I typically buy my puff pre-made (made with butter) because it's good enough and it's hard to make at home... Most people I know do the same. Now granted, making puff pastry is quite a bit more involved than mixing ingredients like a pre-mix cookie recipe but still...
I mean, they were probably all made using convenient measurements that were converted to whatever units you use after the fact.