I don’t think the suggestion is that NASA should go away, rather that - as you suggest - it has far more areas in which to spend money fruitfully than in carrying on with the SLS and its waste -such as the $B to build a new launch platform.
FLCON/Vulcan/New Shephard etc can take Orion to the moon and beyond. NASA can concentrate on areas such as exploratory probes, new space telescopes, and that air part of its name….