The conversion will keep the form of the model shape but to test just apply a standard WAD texture and if it applies, youve got a block geometry construct as models cant be textured in WED.
Then build, you should get a longer build time that if it was a model.

It could be that Blender is creating the extra artifacts as each app has its own format and some would tend to convert files to their own use as MED does by triangulating quads on import.

The idea is to test each of the functions you engage to determin if they suit or are converted poperly.

Standard functions during any dev process will indicate if a conversion actually happened or not by the results you get.

By deselecting convex, there is no need for the app to object to generate multiple blocks to form the shape.

A counter test is to keep the convex and see what results from that.