[Gormo]

I'm afraid that it's you who are wrong on the facts: Congress does not exercise direct oversight over the behavior of these agencies.

Congress passes statutes that establish and grant authority to administrative agencies, and may from time to time pass new legislation that adjusts prevailing law, but they do not intervene to exercise oversight under the current statutes in effect.

That oversight -- evaluating the specific actions of those agencies and determining whether they are within the scope of current law -- has always been the role of other institutions.

Conventionally (and constitutionally), responsibility for for that oversight -- i.e. determining the meaning of the applicable statutes, and deciding whether specific behaviors and actions are within the law -- belongs entirely to the courts.

A few decades ago, the courts decided to abdicate this responsibility, and instead defer to those agencies' own interpretation of the statutes they operate under, indeed having the effect of making them "arbiters of their own authority". This is what Chevron doctrine refers to, and is what the new court decision has finally reversed.