Oh, yeah, they are rendered as polygons with material . Thats why per-Object, you are right . I was thinking about “Object”-s’ management, but considering current Blender’s setup, work on such functionality may be excessive .
In 3D, crossing borders are avoided because of performance, rigging and workspace/view cleanup, this has nothing to do with 2D functionality (which is subject of the topic) . Even in 3D most of objects are made from simple ones, its not expected that you develop a star-constructing function instead or duplicating and turning triangles (2D or 3D) . In 3D i would then execute an intersection function (or use some kind of duplication which does this automatically), in 2D this is not needed .
Current Blender’s setup in regard to the topic’s subject is just a consequence of that someone though that Join is not important for Vector Graphics . Its partially true, but Blender doesn’t operate on 2D canvas, it does on 3D scene . That makes Join needed .