NASA is a development lab
You can't dismiss the fact that NASA is primarily an R&D lab. SpaceX wouldn't exist without the government funded research and development that has happened and continues to happen there. SLS might be the last great NASA rocket but the BFR concept wouldn't exist without the work that's been done on SLS.
Until we have an assembly facility in orbit we will require ultra-heavy lift and we will continue to publicly invest via NASA in developing cutting edge technologies up until the free market enterprise companies actually and fully surpass the public effort. That time will come soon but it isn't here yet.
SpaceX thus far has shown some evolutionary parlor tricks but they still haven't done anything truly revolutionary or taken on any huge gambles like NASA has.