>objectively a huge difference in political plurality in US training material

Under that condition, then objectively US training material would be inferior to PRC training material since it is (was) much easier to scrape US web than PRC web (due to various proprietary portal setups). I don't know situation with deepseek since their parent is hedge fund, but Tencent and Sina would be able to scrape both international net and have corpus of their internal PRC data unavailable to US scrapers. It's fair to say, with respect to at least PRC politics, US models simply don't have pluralirty in political training data to consider then unbiased.