Based on their consumer electronics past, Apple would probably nail the design and get the hardware mostly right. For self driving I think Apple's best bet here to me seems like licensing Waymo tech. Waymo seems to have the lead amongst all and Apple would be more interested in the complete product unlike Waymo which seems to be just interested in the driving tech.
Well, the linked article mentioned Apple's rumored project is being led by Doug Fields, who was Tesla's senior VP of engineering. There are probably others.
Of course, poaching engineers in such a hotly competitive industry seems like could lead to a lot of accusations of trade secret theft. It's sure a good thing Tesla and Apple aren't both famously litigious...
I know people who interviewed for a position there (2018), and it is so covert, that you couldn't guess it was an Apple building until you are literally in the interview room. The building, reception and address had zero indication that it might be Apple.
I live in their area and haven't seen any Apple cars for years, just Lexus' with a ton of sensors plastered on top, which is their self driving team (part of their SPG division).