Either way, Congress isn't a check on the Supreme Court. It's typically rather the other way around.
The Supreme Court isn't a factor at this stage.
"Typically" you are correct. The formal method for checking the power of the Judiciary is for Congress to remove Judges from the bench.
Apple is arguing that All Writs doesn't grant the authority that is being used. If that authority is to be sought then it will have to come from Congress. At least one Judge agrees.
Creation of new works is just such a limit.
If there is not a limit, then what the courts may compel as "assistance" becomes absurd.
This is the argument Apple is making and it is the foundation of the opinion of at least one Judge that has ruled against use of the AWA to compel the unlocking of a phone.