Looking for simple 3D modelling tools

I'm having a frustrating time trying to get some 3D models into Unity. I'm used to modelling programs designed for engineers. Autodesk Inventor is a good example, I can create a sketch, dimension everything to taste, extrude, chamfer, bevel and rotate to my heart's content. Everything is nice and consistent. The game I am working has a nice, consistent style and spacing to its world, I'm trying to model it accordingly.

Unfortunately Inventor cannot export directly to .obj file types, meaning I need another program running, like blender or 3ds max, as well as Unity itself, in order to run file conversions. It's a pain and the time it takes from altering a model to seeing it update in Unity is just plain frustrating. Blender, 3ds max, as well as Unity's new ProBuilder tools, all build and edit surface models. I find their control schemes frustrating and I find the way a model is edited, not as a solid, but as a collection of surfaces, downright impossible. Modeling solids is fantastic, it's consistent and efficient, because adjacent, parallel faces are often automatically consolidated into a single surface. Excess edges and vertices are automatically removed, you can just keep growing your model without all these extra geometric features messing up your creation. What's a good tool I can use straight with Unity that will let me work like this?

(ProBuilder is driving me mental. I REALLY want to love it, but I can't predict where extra or invisible edges will appear, messing with surfaces more than I could believe. It's very unpredictable and inconsistent, at least from my perspective, I can't detect any pattern as to when geometry will be screwed up beyond the point of saving or when it will just "work".)