the SLS is legitimate in so far as it's a bargaining chip for dealing with elon.
obviously spaceX makes better rokets, and has been for a while now.
having their own rocket to fall back on means that elon can't charge whatever he wants for future missions.

remember when he got mad at trump over the epstein thing and threatened to leave those astronauts on the ISS?
that's what he does when you're crew draggin your feet developing a system that works.
most of the time spaceX's shit is really good though.