Depends on how much you explain them, really. In TES the Dwemer ruins first appeared in Redguard (if I remember right) but Morrowind massively expanded their lore, but managed to do so without diminishing their central mystery.
I’m hoping for some similar treatment for the Temple creators. Or at least an explanation that raises more questions than it answers.
It’s kind of new thinking in the games world. Todd Howard has said that if they’d anticipated Skyrim’s enduring popularity, they’d have released a lot more DLC for the game. Instead, they put out two DLC plus a home-builder addon and then moved everyone to Fallout 4. Which probably seemed like the best use of resources at the time.