Given that several companies make advanced chips, but no companies have ever made fully reusable rockets or achieved SpaceX scale, I think Starship is harder, but we shall see.
Terafab will technically be two fabs, each making only one chip design. This greatly simplifies process flow and allows more linear, adjacent movement of the FOUP.
A super high production rate allows us to test very quickly what steps can be deleted, simplified or sped up, even after the design is fixed. Current fabs are extremely conservative, operating on rigid historical heuristics, which are mostly, but not all, correct.
Anything that is a rate limiter at the machine level means that machine will be redesigned, unless already at limit of physics.
Having new iterations of a chip design be produced every day in the research fab (with <7 day lag) means being able to try out many high risk, high return ideas.
Etc
In any event, there is no other way to reach extreme scale, so either we make Terafab or we will be stuck at the ~20% chip/memory output growth per year of the current industry.