The hard part bout building an electric car isn't the electric part, it's the car part. It's build quality that's hard to get right and has to be earned with sweat equity.
Almost every Tesla I've ever seen up close had body panel gaps that were about as uniform as as those on a fiberglass kit car with a VW chassis underneath.
And build problems Teslas overall probably aren't any more numerous than other manufacturers, it's just that Teslas are so chockablock with bleeding edge technology that the failure of any one element of that technology is spectacularly obvious. Like roofs that fly off while you're driving down the expressway. Autopilot that runs over kids. Batteries that explode with no provocation and burn for days at 3000°F. And door handles that don't work if the car is underwater or on fire.
Build quality is easy to get right. The only reason rivion or tesla have these issues is because they have no experience building cars.
The hard part about building an electric car is building something practical with range and quick refuelability. Doesn’t matter how good or reliable your electric motor is, if you need three tons of batteries to give it over 300 mile range, you’re gonna have some issues. If every fillup takes an hour or more, the car’s not gonna do that great. If every ten years you need to replace a major component that costs over half the value of the car, it’ll have problems.
The issues aren’t in the build, it’s in the practicality of the tech. Just not completely there yet.