Tesla, at bill profit, is about half an order of magnitude away from being in the top 10 most profitable: https://www.investopedia.com/the-world-s-10-most-profitable-...
So surely a successful company. At this juncture, one of the most successful ever in existence? Hype.
Now, I'm not saying that Tesla is not on their way, but they are not yet there
None of that matters compared to the fact that he is the largest shareholder.
Owning 9% of a company's stock still gives a lot of votes. 10-20% is enough to enable an activist investor to really be a pain for a company. Even as little as 5% is enough that the SEC requires special forms to be filed because of the power that gives to an individual shareholder.
Elon presumably wants influence over Twitter, without the responsibility of running Twitter. He can get that with a lot less than 50% -- in fact he may have already achieved the level of influence he wants, and one sign is that Twitter feels the need to make public statements about it.