SLS took 11 years to first flight and cost $29 billion. First flight was perfect and went around the moon. Starship is estimated to have cost about $10B so far and has had 11 test flights and still hasn't achieved orbit.
SLS can reach the moon from the earth, Starship can't reach the moon on a signel flight and requires 10-40+ tanker flights to fuel one lunar mission. That's a lot of chances for failure.
Even after Starship finally achieve orbit, it's still years away from being able to attempt what SLS did on day one.
The claim is that Starship will eventually be cheaper because of it's re-usability because they target $10M per flight you are talking about $400M for a lunar mission. But $10M per flight is insanely unrealistic. Consider that the Falcon Heavy, which is much, much simpler than Starship, costs around $90-$150M per launch. If we generously assume $50M per launch and 15-20 tanker flights that's around $750M - $1B which is suddenly comparable or could be more expensive than SLS.
Considering that SpaceX does not currently have a fully reusable rocker and if they manage to make Starship fully re-usable each one would need to be spread out a huge amount of flights to start becoming economical.
What's obvious to me, and maybe not everyone here, is the design of Starship is optimized for LEO, not deep space missions. The re-usability features are earth-specific (heat shield tiles, flaps for atmospheric control, landing legs designed for earth gravity). All of this mass is dead weight for a deep space mission.
Notice the HLS variant of Starship depot ships don't re-enter the earth and don't have all this re-usability stuff.
The refueling requirement is a consequence of the design. Starship is too heavy to reach the moon on one launch. It's massive dry mass prevents it from leaving LEO without refueling.
It's design is also not optimized for Mars either. It's optimized for earth operations. Mars has only 1% of the earth's atmosphere requiring completely different aerodynamics. You still need orbital refueling to get there and also back. It needs in-situ propellant production on Mars just to return to earth.
All of this is enormous complexity that hasn't been even close to being demonstrated (remember, Starship still hasn't achieved orbit).
What they are doing is building a ship to deploy Starlink, and wasting NASA funding to do it.