If I look at a BYD at my local dealership, and compare it to a comparable spec German car (I live in the UK, so tariffs are not the thing shifting the needle here), I can see where the cost savings are and the trade-offs.
I don't think they're artificially more affordable. I just think they're more affordable.
Using public funds to invest in capital expenditure is - outside of the US - considered a wise use of public funds. If the result is a more competitive industry, whether that's ship building (South Korea), steel production (recent UK nationalisation efforts), military hardware (United States), or medical research, physics, chemistry, computing (look at the history of all the G7 there), and so on, and so on... irrelevant.
China has decided to spend it on complex manufacturing that they've been the supply chain for to Western manufacturers for the last 30 years. That's not controversial - it's been obvious this is where they were heading for some time.