I build a LOT. I got bored with the simple "ikea" design quickly, so I want to, for example, take the pieces of ikea furniture, throw out the instructions, and build something completely new with it. Something that it wasn't necessarily designed for. Again, I only build houses to look cool, not to be playable, so to me it doesn't matter if a feature I make is useable. To each their own.
By "genuine" I guess I mean "more challenging" - not to actually build something, because obviously things are much easier to build in Sims 4 - but to build something NEW. I loved Sims 3, but to me they're very different games in terms of building. In Sims 3, building is like an architecture project. You have all the tools you need to make something interesting, just like in architecture. In Sims 4, it's more like a puzzle - figuring out all the different ways I can use the limited tools to make something interesting, something others might've never thought of before.
Again, this thread is unpopular opinions, so I know this isn't a popular idea. Like you said, most people would say it's much easier to build in the Sims 4. I'd agree, but I'd say also that it's much harder to build something interesting and new.