Section 230 is not and cannot be the be all and end all with respect to (allegedly) protecting platforms from liability with respect to content providers, no matter its merits or deficiencies. And it ought to have applied to Parler since AWS threw them off the web on the basis of claims with respect to content creators.
You aren't understanding what 230 does. It has absolutely nothing to do with what happened between AWS and Parler. 230 is simply about liability protection, nothing to do with business contracts or relationships.