Yeah, one could certainly argue that USBM, French BM, Polish BM, Slavic BM, etc., are all incarnations of the 3rd wave. The problem still is that these groups mostly lack coherency musically and ideologically. The musical differences in the 2nd wave are mostly overcome by ideological similarities, but even then, there are plenty of bands that we lack sufficient judgment to assess in this way.
I would give more credence to 3rd wave bands that isolated themselves from the specifically Scandinavian elements of the music, namely the focus on "coldness", and later on pagan elements. Coldness is something not really found in the Slavic BM releases, and in most of the more original USBM releases, which find some coherence in their focus on isolation, and more of a departure from religious themes. Only the knockoffs in USBM really focus on the whole coldness theme. I don't know enough about the French scene to assess what's going on there, and how it relates to France.
The best way to define the 3rd wave to me, would be to include bands that showed substantial influence of national character. So within each scene there are bands that are doing something uniquely native, and bands that are strictly aping the 2nd wave, and degrees in between.