There were many terrible electric cars out of China for years. Every province had its own little EV manufacturers. China's car industry is less concentrated than the US, but the big players are winning.
BYD is only the 9th largest carmaker in China. SAIC, Changan, and Geeley are the top 3. SAIC and Changan are state-owned, but Geeley is private, as is BYD. SAIC makes about 5 million vehicles a year. General Motors, over 6 million. BYD, around 3 million. Tesla, a little less than BYD.
Reviews of newer BYD cars are quite favorable. It's not like five years ago, when China's electric cars were not very good.
BYD has a simplified design for electric cars. The main component is the "e-axle", with motor, axle, differential, and wheels in one unit. There's a power electronics box which controls battery, motor, and charging. And, of course, the battery, made of BYD lithium-iron-phosphate prismatic cells. Talks CANbus to the dashboard and driver controls. BYD offers this setup in a range of sizes, up to box truck scale.
BYD and CATL are spending huge amounts of money to get to solid state batteries. The consensus seems to be that they work fine but are very hard to make. The manufacturing problems will probably get solved.
(Somebody should buy Jeep from Stellantis and put Jeep bodies on BYD E-axles. Stellantis is pushing a terrible "mild hybrid" power train with 21 miles of electric range, and an insanely overpriced all-electric power train. Stellantis prices went through the roof under the previous (fired) CEO, and sales went through the floor. Jeep sales are way down, despite customers who want them.)