No idea what the problem could be, but I would think it has more to do with Blender itself than the import tool. Did you freshly install Blender? Maybe remove all (previous) settings? I'm not a big fan of the Blender UI either.
I just did a new test, this time at a higher (4K) resolution: https://i.imgur.com/NFyP0eA.png
I disabled the concave walls and enabled the brick seams. Looks pretty nice, although the lever parts look a bit rough. One halve is smooth and the other halve still has visible polygons, which creates a very weird look. And I think I have to slighly lower the brick seams.
I just did a new test, this time at a higher (4K) resolution: https://i.imgur.com/NFyP0eA.png
I disabled the concave walls and enabled the brick seams. Looks pretty nice, although the lever parts look a bit rough. One halve is smooth and the other halve still has visible polygons, which creates a very weird look. And I think I have to slighly lower the brick seams.