- More expensive than Starship, or
- Took longer to develop than Starship, or
- Are significantly less ambitious than Starship
(and those are definitely not exclusive ORs)
- Not sure where you're getting the SLS number, the GAO report at https://www.gao.gov/assets/gao-23-105609.pdf claims, "Since 2011, NASA has spent $11.8 billion to develop the initial SLS capability."
- I think the marginal cost is a fair question. The whole party line out of NASA was that this time Moon exploration would be sustainable. If each trip costs > $1B before you even put a payload on the rocket that's a big problem.
SLS use leftover engines from the Shuttle era. Yet it still cost 160 millions. Each. Thrown away after each flight.
Vulcan is a conservative design with no reuse. It also uses BE-4 engine, which costs them nothing to develop.
Space flight is hard and different testing methodologies are no silver bullet. But, I suppose we will know them by their fruits.
It is quite a manipulative word to use.