No, France does the same thing, it has much more high speed track than Germany, even though TGVs ride on classical track as well in the periphery.

I don't think so. There's simply too much traffic on the shinkansen lines to be able to mix slower and/or freight trains on the same lines. On the Tokaido line between Tokyo and Osaka, trains run every 7 minutes (IIRC); you can't have a freight train sharing a track with a bullet train service that has trains that close together.