I feel like Bethesda built a neat mechanic into the engine, the in-game building, but then never did much with it. Yes, you can build a settlement, but the actual task is mostly pretty basic, not much integration or planning to it, and could be a bit grindy.The Sim Settlements 2 mod to which I assume you're referring did a better job, though I still feel like one could do far more with player construction than has been done in any of:
Vanilla Fallout 4: layout matters very little, building is mostly a sandbox for aesthetic fun, not much by way of layout decisions other than making some more expensive things harder for raiders to hit. Does have the "The Castle" fight, but that's short and about it for a real fight. Kind of grindy. Can get aid from the Minutemen if a settlement is nearby with th flaregun mechanic, though that's pretty minor and I never bothered. Get some settler-produced resources which don't matter. Get a sleeping spot, which can matter in hardcore mode. Not Sim City or Caesar in 3D.
Fallout 4 with minor mods: can remove more items in an area to get a cleaner look; some of these break precombines, which hurt engine performance. Can build anywhere, not just in settlements. Can break the restrictions imposed by vanilla Fallout 4 on number of items that can be built (which keep performance sane).
Fallout 4 modded with Sim Settlements 2. Does a better -- albeit still kinda sketchy from a story standpoint -- job of incorporating building into the game, has a storyline and quests. Eliminates the grind aspect -- you can just take a settlement and let the settlers do almost all the construction, and get much-more-elaborate reconstruction of the Wasteland then I'd manually do. Does some rebalancing so that the weight on the Local Leader perk to make settlements trade, a major QoL improvement, is basically free. Gives me more of a feeling of progress. Plays reasonably well with people doing manual construction alongside the computer-driven stuff. More-substantial automated production. The randomized stuff malign what shows up something of a surprise helps keep it a bit interesting. Makes the game feel a lot more active. Still doesn't have a lot of gameplay around layout.
Fallout 76: Player CAMPs are very important to the game, as they contain essential equipment, and defending them is important. Still not a lot to the layout in terms of gameplay. Some people (not me -- I'm in the "floating platform" crowd) really enjoy doing realistic and aesthetic CAMPs, and it's a way to help put a very limited form of player-driven content creation into a form where everyone can easily enjoy it. Player vending machines, scrapboxes, respec locations, and workbenches (to create scrapping locations for overloaded players) create a reason for other players to visit and see them. Extremely limited automated production of certain resources -- if you want some very specific builds, like Nuka-Cola-based weaponry, automated production might be useful, but in general, it's not worth your time.
There are player Shelters as well, "underground" or otherwise off-the-main-map mini maps that players can own and build freely in; there are entered from various entrances created in a player CAMP. I think that this was intended to leverage a survival aspect of Fallout 76 that was originally intended to be a lot more important -- radstorms, and needing to seek shelter. These are so infrequent and weak, though, that by the time one gets to Shelters, they're essentially ignorable. Nothing in a Shelter can be attacked by raiders, but automated production does not work in a Shelter.
With a subscription, there are placeable Tents that can be put on the map in places not one's CAMP. These provide a resting, scrapbox, and scrapping location that can exist anywhere. Helpful QoL to stick near boss fight locations.
Bethesda sells cosmetic items, if you like that sort of thing (which based on EA's sales of items for The Sims, I assume some people very much do like). Not very much potential for modding here, due to it being a multiplayer game with the servers run by Bethesda, so unless Bethesda gets and decides to plunge a lot of money into it, vanilla Fallout 76 is probably about as much as there's going to be.
Starfield. Meaningful automated production system and resource-hunting system, with slightly more-interesting layout and defense. The problem here is that the only real gameplay reason to build bases is to...get lots of resources, which are only really useful to build large bases. It lets players who don't like building skip that aspect of the game, but at least to me, made the building aspect feel kind of pointless and circular. We'll see what happens with mods. The engine is good, and there's potential for interesting things to happen, but if they don't get created, well...
I mean, it's fine as a stand-alone game, and selecting and setting up a collection of mods takes longer than I'd like. I kind of wish that the default starting point was to do something like what Wabbajack does, use a large curated set of mods, but then let one tweak it like the regular mod managers. But Skyrim and Fallout 4 have to be some of the most-modded games out there. It's a lot of content and improvements from the community.
They also released some years back. Without mods, they look kinda old in present-day context.
I mean you do you, but Beth games are modding playgrounds, the only other games I can think of really is Rimworld. So for me, playing a Bethesda game modless is like eating a sandwhich of white bread and mayo