Unity
Ah. I see the situation now. Unity makes it really easy to get a model to walk around a plane, or whatever terrain plugin you use. After that it's a massive net productivity loss for software developers. Sure, it's great for artists who don't really understand any code, but it's an anchor chain around the neck of a developer. You have to do things Unity's way. You can't just change core data structures or engine loops willy-nilly. There's a massive complicated pile of junk that you don't need integrated into the parts you do need, regardless of which things you need. This gets in the way and slows you down and frankly is a demoralizing clusterfuck. This is why all the new indie games coming out are disjointed piles of plugins and store-bought assets. This is why the "release" of Manor Lords wasn't really that much improved from the early access demo. This is why Valheim development essentially stalled. (And they still haven't fixed the horrible LoD popping.)
To be clear, it's a problem of using an "engine", not a problem specific to Unity; you'd have the same issues on Godot, Unreal or Lumberyard.
Lean code lets you iterate fast. If I want to test out a new feature, I just write a quick function and hack it in to whatever existing location makes sense. If it works, great. If not, rip it out. When I run into performance problems with it, then I optimize it.
This comes at the horrible cost of having to learn OpenGL and how a GPU works conceptually and writing a bit of boilerplate. That's maybe 10% of a 2D game, especially if you use existing libs to do things like load meshes into memory. Even in 3D it's smaller than the gameplay part, though everything is more complicated in a 3D game.