The biggest challenge with the comparison is STANDING.
Almost no one would be granted standing in a lawsuit against the debt cancellation. The government owns the debt due to the restructuring that occurred years ago, and so the government can plausibly forgive that debt.
With rent, every landlord will have standing. Such a proposal automatically becomes a “taking” that is unconstitutional according to the Bill of Rights. In order for it hold, the government would have to pay the landlords, and that could easily amount to trillions of dollars.
Indeed. That's one of the biggest scams the court uses to avoid hearing cases. That, and 'ripeness'.