I mean, you offered a basically similar, implausible counterfactual. I think we can agree that it is at least parties that the EU would have opposed purchases of Chinese, Russian or Iranian weapons by the USA and vice versa -- but Russia and Iran have been sanctioned for long periods of time (Iran, basically continuously) by both the EU and the USA, and Russia is the main territorial threat to the EU, so maybe only China is really an interesting possibility here.

Arms trading with China is probably not a good idea at all.