The original TBC at the tunnel across the street from SpaceX was a proof of concept that used essentially off-the-shelf tunneling tech so that the team could learn how the current state of the practice was accomplished, and that they could improve on it.
I don't know if you're familiar with tunnel boring (and if you are, sorry I'm explaining something that you probably know better than I do), but essentially the phases of digging, mucking, and reinforcing are not done concurrently, and I think that was the first things they were trying to do, and then move on from there. But yes, smaller tunnels were part of it.
Also, they did not do any real innovation, as you seem to be claiming. Combining those steps is 50-year-old technology, at least, and has been done at scale (ie not on tiny tunnels) many times.
I always thought Boring was a project intended for digging a base on Mars, fitting a whole Tesla in the tunnel would be even more than what's needed to connect some underground habitats.