The SLS is not a commercial launch vehicle, and does not in any way serve the same role as the Falcon 9. If you need to launch payloads that big, it is essentially the only game in town for now. In any case the launch cost estimates for SLS are pretty handwavey and incorporate a lot of r&d.
The Falcon 9 is clearly not 90% cheaper than launch vehicles of a similar role, ie ~20 tonne commercial launchers.
That's never had a successful real-payload orbital launch, and its figures should be treated with even more suspicion than Ariane 6's. If and when someone can pay for a launch with a defined time scale for 10% of the real cost of SLS, then, sure, okay. Until then, it's marketing.
The Falcon 9 is clearly not 90% cheaper than launch vehicles of a similar role, ie ~20 tonne commercial launchers.