The point of the Chinese tariffs is precisely to prevent companies from BYD and Geely from killing American automakers with their cheap, low-quality cars.
(BYD, for example, is notorious for the abysmal quality of its electric busses, which are so bad that they're now effectively banned from consideration by most American public transit agencies. A SoCal agency bought several dozen busses a few years ago; only a single bus survived a year without major problems. Contrast that with their ICE or natural gas counterparts, which last decades.)
They are also heavily subsidised by the chinese government. If you think this through a bit you notice that you loose a war if you kill your national automakers and are dependant on china. Also look at Germany, they are still struggling, as they don't understand the market at all.
If they are so low quality, then let them in and let them fail in the marketplace. I don't think they are so bad. Fleet buses are basically a completely different business btw, that has really nothing to do with private car quality, and besides that, I have a hard time believing BYD buses can be so bad. Probably the SoCal place got an early generation but with the volume they are doing world wide, it's just nonsensical to think it's all garbage.
Manufacturing is tied to national security. Even if those cars are of terrible quality, the Chinese government can subsidize them (they already are) to the point they are valid competitors to normal quality cars. On the surface, this is a win to consumers as this would drive down prices and expand options. But to the US government, this would kill many automakers and factories and reduce national production capacity in time of war.
A very significant factor that allowed the US to completely dominate WW2 was its intact infrastructure and the resulting high manufacturing output. When you churn out ships and tanks in matter of days while your enemy, even with superior technology and quality, takes months to do so, you win. Japan's ships were incredibly well built but they lost the war because they can't replenish fast enough.
(BYD, for example, is notorious for the abysmal quality of its electric busses, which are so bad that they're now effectively banned from consideration by most American public transit agencies. A SoCal agency bought several dozen busses a few years ago; only a single bus survived a year without major problems. Contrast that with their ICE or natural gas counterparts, which last decades.)