The complexity with the Executive Chairman -> CEO -> CTO sandwich is that Elon also has a day-to-day operating role at the company.
That means that he's visible in the office (because bye-bye remote work), and when there are product/technical questions, it's unclear to employees whether Elon or Linda is the ultimate decider. It's normally not a problem that the board can fire the CEO, because employees never interact with the board and often don't know who they are. But when the chairman of the board is also an ordinary employee, some fraction of employees will follow the official reporting structure and do what the CEO wants, while some other fraction of employees will follow the "power behind the throne" and do what Elon wants. The result will be a company that can't agree what it's doing, with multiple competing groups working at cross purposes.
This was a huge problem at Google, both in the early days and today. Larry and Sergey would go directly to engineers with ideas, and then those engineers (hoping to get a coveted Founder's Award, and out of respect for the founders) would drop what they were doing and work on Larry's ideas. It worked in the 2000s, because Larry & Sergey's product judgment actually was really good - that's how we got GMail, and Chrome, and YouTube, and Android. But it's also the root cause of much of the organizational dysfunction that affects Google today. Google culture follows competence, not reporting lines, which means that one giant company is actually 1000+ small groups of unrelated projects, most of which duplicate each other, that never integrate quite right, which will often be technically brilliant but then blocked or unlaunched as soon as they cross some competing executive's path.