The validity of the comparison aside, if Apple had bought Tesla in 2013, I feel pretty confident Tesla would be worth more now than it is.
That said, if Elon Musk had taken over apple from within (like steve jobs did via next) apple might have gotten more interesting.
Elon Musk is certainly innovative, but he's certainly not a saver. He seems to like to take resources to grow as quickly as possible instead of growing at a controlled, steady pace like larger companies do. Basically, he's more "go big or get more funding" than "slow and steady wins the race".
Jobs was pretty good at design and hyping up modest improvements. Elon just wants to wow everyone.
This is one of the Apple "secret sauces". Want Gorilla Glass? You get me the latest gen exclusively and I help you build your factory.
Tesla cars are first revision technology, which means almost starting from scratch anyway.
Two companies that live on reputation instead of quality would tarnish both.