And they have really good designs (after all, they are taking inspiration from the most succesful european cars. I saw the station wagon the other day, it's amazing. the octavia EV as it should be.)

The problem is always going to be: what's going to happen in 10 years, or whatever, after warranty expires?

The problem with vertical integration is for the customer, and it's repairs: traditional manufacturing is more expensive because you have a constellation of companies manufacturing pars with official and unofficial second sources. While this increases the overall cost of the vehichle, it decreases the final price of every component because the customer (independent mechanic) can choose to use a different source. The market working as intended.

BYD is currently the only EV i would consider, because it's the best value and the engineering quality is indeed high, but because i want to own, not rent, i'm preoccupied of what's going to happen in X years.

Yes, it's the same fear we had three-four decades ago when toyota/suzuki/kia entered the european market, that bet paid off but also because cost of repairs went down over time as they were also traditional manufacturers. (Yet for some exotic components you still must go to the OEM, and pay 2-3 times the equivalent sensor/component for an european car.)

However, with vertical integration you are always at mercy of the manufacturer. Better engineering, yes. Better integration, better efficiency, but you will suffer for repairs if you can't have second sources.

Think apple. (and tesla. but tesla is shit quality)

Or john deere.