I'm not a huge fan of Parler, but hopefully this move pushes the government to force Apple to allow alternate App stores and/or side loading. People should be able to run Parler on their phone if they want to, with full API access, not the half-measures that having a web app allow.
Under what justification?
These people agreed to the contract. Their BATNA is Android, which allows sideloading, or their web browser, where they can be as unmoderated as they want to be.
There is no problem here. If you want an Iphone supporting app store with more permissible side loading, go build one.