Settlement building was also provided via mod in Fallout 3 and Skyrim, although there is a line between "a mod did it and Bethesda stole it" and "a mod did it because the idea was popular and bethesda also implemented a version because the idea was popular"
To me, theft of this nature requires more then "a mod did, and so did they, so therefore it's stolen". Imitation isn't theft. Theft would be taking the actual code and design decisions and using them directly (which they may have, I'm just saying ti takes more then 2 things having a similar scope/idea). And in my mind, if Bethesda takes the best and most popular ideas from the previous generation of mods, and adds them to the core game, that's better. We're a vetting ground for ideas that are popular vs a waste of their time. and I'm personally fine with that.