[tsimionescu]

Only if the SuperHeavy booster can achieve the same performance as the SLS (payload to orbit), with similar levels of operational complexity.

The SLS has already proven it can fly to lunar orbit and back on one single launch. In contrast, even if everything goes according to plan, Starship requires at least a dozen re-fueling flights while it hangs in orbit around the Earth to be able to then fly to the Moon.

Will one Starship launch, when it eventually works, be cheaper than SLS? Very likely. Will 12+ Starship launches + the time in orbit be cheaper than a single SLS launch? Much, much less likely.

[NetMageSCW]

Actually, we already know that with booster reuse disposing of 12 tanker starships will cost less than an SLS launch and actually be able to get to the moon, which SLS with Orion can’t actually do.

[tsimionescu]

We don't, because Starship has not had even one successful flight with any appreciable payload. It's absolutely possible that the booster will need to be completely redesigned, and become much more expensive, in order to achieve the mission goals.

It's also worth noting that a captured booster has only once been successfully flown again - and certainly not in the kind of tight time line that the in-orbit refueling operation requires (first flight was March 6, second flight was October 13 - and no more flights are planned anyway). There is currently little proof that boosters can be "rapidly and fully reused" as needed to match any of the cost promises.