I generally use: - Overbuilt: Designed to handle more of the same. Too strong. - Overengineered: Complexity not justified by the requirements.

Sometimes overbuilding (e.g. using really thick wood on a treehouse) means you can lower complexity (less bracing needed) at the cost of being more wasteful with material. That is often a great tradeoff.

I think your concrete treehouse counts too though. Add a shower and suddenly you need plumbing, drainage, the structure has to hold more weight. The overcomplicated part drags the overengineered part along with it. They pretty much collapse into the same thing.

Reminds me of the Seinfeld episode where he hires a contractor to work on his kitchen and ends up with twice as many cabinets as he had before.