You're not taking into account future emissions. If everybody stopped buying PV cells from China, that would severely retard the development and rollout of PV, and so cause more emissions.
Not sure. PV generated electricity is around one percent worldwide. CH4 and coal thermal stations have the lowest investment price per kW, so booming economies won't invest massively in PV until CH4 and coal get very expensive. Add to that that PV is very dependent on geography and does not work at night, to make it more than a day peak adjustment you have to also invest in batteries that cost even more carbon-wise.
China is not the only country which produces PV panels. PV panels are also not the only choice in alternative energy. If one is interested in reducing carbon emissions, it's so much more complicated than "just buy solar".
