SO SE used to put some "hard-to-get" cards on NPCs in a manner that sort of made sense. Think about Eureka (not the dungeon). I think each of the "zone bosses" dropped cards at a low chance if you killed them when they popped. If you finished all of the Eureka content available (not including BA), in the next expansion, the cards were on NPCs. And if I recall, those NPCs had pretty strong decks or very frustrating match rules. And that was a good balance.

They also put some other hard-to-get cards on NPCs as well, such as the 24-man cards from the Stormblood era. I think those are also on NPCs in Kugane.

I was disappointed to see that we made it to the end of EW and I don't think they've added many "alternate ways" to get certain cards (looking at your Copied Factory).

If SE's plan is to make another TT mount for having all of the cards from 313-4XX, then some need to be locked behind certain content to give "value" to the mount. Think of the cards locked behind blue mage. It "forces" you to do content that you wouldn't have done otherwise. And in some ways, that's a good thing.