The EU does seem to willing to reduce itself to a Chinese vassal. That would not improve the situation.
> The EU would also have opposed it if the US bought Russian, Chinese or Iranian weaponry.
This is such an implausible counter-factual that I can't even begin to imagine what would have actually happened. Still, I doubt any more than some "public letters" would have been issued, whereas I'm sure that the opposite would have resulted in actual economic pressure from the USA against the EU/NATO country that would have dared, under any administration.
Arms trading with China is probably not a good idea at all.