In terms of the WORLD, then it's definitely Japanese music. No doubt in that.
Just Ayu alone has a larger scope than any Chinese pop artist I know in her generation.
However, if you're speaking quantitatively, as in, in terms of how many followers or fans they have in total, I have to say that because China has such a large population, some Chinese musicians are really influential just in China alone.
There's no real need for them to expand their target audience really.
And the points about mainstream Chinese music being bland and uninspired isn't exactly false. XD There's no real Ayu equivalent in Cpop, a musician that bears his or her soul in their lyrics! Just doesn't exist. IMO, everything feels really fake here, and the mainstream artists only go famous for a while and then fail afterwards. This doesn't apply to everyone as obviously there are some pretty classic artists here like Faye Wong and Teresa Teng... and hmm, Roman Tam, Sam Hui, etc etc. They're all part of the "oldies" though, except Faye Wong, haha.
Even if we're including Taiwan-pop into the equation (which is still Cpop I guess) I still hold my opinion.