That doesn't make any sense. "Legacy auto" knows how to make cars. To their final assembly factories there's not a huge difference between a BEV, PHEV, or an ICE drive train. So long as they feed in components they get cars out. They definitely know how to get components made to feed into their factories.
That's a place where they have an advantage over Tesla. They can make BEVs that break even or lose money because they have a whole line of ICE cars making a profit. Tesla only has their up market BEVs to make their money.
Tesla doesn't have a moat around BEVs. Now that "legacy auto" is making them Tesla is just another BEV manufacturer. As their market share erodes they're going to have a harder time maintaining their price premiums. They also don't have the deep bench of fleet sales that "legacy auto" has. The places they're trying to diversify (Power Wall, solar, etc) aren't markets that support the premium prices they currently enjoy with their cars.