Hell any home 120v wire welder can do mild steel. It is the cutting and shaping part that is hard.

welding aluminum requires TIG. It’s harder and more specialized.

You can weld aluminium with MIG just fine. It is indeed way more difficult than normal steel and not every car shop has skills nor equipment for it.

TIG is neither expensive nor difficult any more. Laser welders are now cheap and trivial to use for aluminum.

Fair enough, I may have inferred a bit too much, so here is what the CEO said:

And so third parties, the reason you saw some of these really high numbers, is we’re like, ‘A Rivian? And what’s a Rivian?’ So they they don’t know the car, and they quote an enormously high number, the insurance company agrees to it, and then that happens.”