The candidates you listed shows that it is a genuine attempt at soft power. Just because it's soft power directed to people we don't like doesn't mean it isn't soft power.

China is using their "peace" prize as soft power to further their own interests. They are being rather blatant about it as you showed with mugabe winning it in 2015. And europe is using their "peace" prize to further their own interests. Though they do pay lip service to "peace", "human rights" and "democracy". The chinese haven't bother with that much, but if history serves as an example, it won't be long before the chinese pretend to be the champions of the "peace", "human rights" and "democracy" like europeans do.

Also, the chinese peace prize winners are suspect for sure. But so are the european peace prize list. People like woodrow wilson and henry kissinger are nobel peace laureates.