Stephen Miller worked the DHS and HHS the way you described in the first Trump administration. Presumably Biden had ample time to “seize these levers” no?
Biden chose not to use the power available to him to its full extent. He could have done something really extreme with the immunity he was granted by SCOTUS, but instead, he disavowed it.
Don't fall for the "us vs. them" distraction. This is about seizing power, not Democrats and Republicans.