None of the tech "developed" for SLS, Orion or Gateway would be useful for anything Mars related. To clarify - significantly useful, or reasonably priced useful. That's a dead end program.
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.
New information on long term deep space radiation exposure, new information on long term space travel in general. Lunar research not done before, now possible due to lunar research station. The list goes on and on. You can look up all research projects included in the Artemis missions online
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.