I personally think that it is a must to go to Moon first before any attempts at Mars, and dead end program can be a reasonable price to pay for the necessary iterative research. But SLS specifically is super bad and super expensive at that task. If the Starship program would fail for any reason but NASA would continue, I think after SLS will finally die, another, totally different system would be required to go to Moon again, to finally iterate on it to go to Mars next.

Basically humans are wasting time with SLS, and would need to repeat a lot of efforts again, to continue human space exploration.