I'm not sure if your comment is meant to be snarky. But seriously... What is Elon doing differently?
The original Tube tunnels actually have several problems - the tight diameter means that air conditioning is basically an impossibility (no room for the equipment in vehicles and nowhere to output the heat), and it makes maintenance and emergency evacuation annoying and hazardous if you can’t have a walkway for people to walk alongside the trackway.
I have seen articles about it, as well as a recent proposal to use that heat for heating homes. But it just illustrates the (many) potential pitfalls of small diameter tunnels, because you really don't want your tunnel to become an oven after a few decades of heat generated from braking.
Other pitfalls include:
You need space for adequate ventilation. This is less of a problem with electric propulsion, but you do still need it for emergencies (like a fire). And then there's the issue of noise; if your vehicle is too small compared to the tunnel, then the air being forced out once you get to a larger space (like the outside or a station) creates loud noise. Japanese high speed rail trains have much stranger aerodynamic shapes than European ones because they built smaller diameter tunnels and this ended up causing noise issues at higher speeds.
There are plenty of ways to slice and dice this number up but the short version is that this is not faster than how the original TBM performed (let alone 3x) - I know the guys that Elon bought the TBM from and the guys that those guys bought it from.
As I’ve said in previous posts about this, TBM operation is not the limiting factor in building a tunnel. Permit acquisition and third parties are the longest part of tunneling projects by far.
The only reason Elon thinks he can make it faster that I can divine is engineering magic.
Given his track record, I'm inclined to believe he understands the problem space and how to solve it better than you or I.
Yes, the burden is on him to execute, but that will take him years. The argument that "I don't understand it therefore it's invalid" holds little meaning. Musk isn't a person who gets this deep into a project without a high likelihood of success, historically.
Elon Musk has a practically unbroken track record of making wildly speculative, overconfident promises about all sorts of technologies that never materialise, and gullible people lap it up like it's going out of fashion. People are dying because of Tesla's irresponsible and misleading marketing, and Musk shouldn't get a pass just because some people think he's a visionary.