I am sorry. I have to disagree to some degree. This is not an apples and pears or apples and oranges comparison at all. Comparing 3DGS to something like Wintermute would be, but not Unity and 3DGS.

What you just did was compare the TOOLS (editors) and the methods the engines use to manage a scene. But both engines are real-time 3D engines. Both can be used to create FPS games (for example) and, as a result, both can be compared on an "apples to apples" basis. In the comparison, the exact things you brought up would factor in: the tools that come with it (editors, etc), the programming languages used and scripting language (if any), the type of scene management, if it includes things like a physics engine, etc.

If comparing Unity to 3DGS is an apples to pears comparison, then 3DGS cannot really be compared to DarkBASIC, Torque or any of the others out there either and, as a result, 3DGS will end up being the only "apple" in the cart.

And, no, you don't have to create the same project in the same engine to compare them. Not at all. The engines can be compared BEFORE HAND to determine if any engine can be a candidate for the project at hand. Else a development team would have to purchase several engines and recreate their project over and over again in each one in order to meet your criteria for comparison.