I like how Rutherford responded in Lex Rex, respecting the "legal" argument of powers, enjoining the king's supremacy with the power and authority of the parliament of Scotland, past.
See especially, question 43 Assert. 2, which reads,
"The king, at his coronation, (Parl.1, James VI act 8,) swears "to maitain the true kirk of God, and religion now presently professed, in purity, and to rule the people according to the laws and constitutions received in the realm, causing justice and equity to be ministered without partiality." This did king Charles swear at his coronation, and was ratified, Parl 7, James VI act 99. Hence he who, by the oath of God, is limited to govern by law, can have no prerogative, or rather supremacy, (enacted Parl. 8, James VI act 129; Par. 21, act 1, James; and Parl.1, Charles, act 3,) cannot be contrary to the oath that king Charles did swear at his coronation, which brings down the prerogative to governing according to the standing laws of the realm." It cannot be contrary to these former parliaments and acts, declaring that "the lieges are to be governed by the laws of the realm, and by no particular laws and special privileges;" (but absolute prerogative is a special privilege above, or without law

which acts stand unrepealed to this day; and these acts of parliaments stand ratified by Parl. 1 Charles, 1633."
The "standing laws of the realm" are appealed to by Rutherford, which reduces the king's royal prerogrative, or rather supremacy, to that which is limited and not contrary to previous laws enacted by parliament.
King James VI of Scotland reigned for 36 years before also becoming King James the first of England, when the union of the crowns met with one king over both in 1603.
Assert 3, reads, "Parl. 8, James VI in the first three acts thereof, the king's supremacy, and the power and authority of parliaments, are equally ratified under the same pain: -- "Their jurisdictions, power, and judgments in spiritual or temporal causes, not ratified by his Majesty, and the three estates convened in parliament, are discharged." But the absolute prerogative of the king above law, equity, and justice, was never ratified in any parliament of Scotland to this day."
Representatives are to regulate the power of the king. King Charles I gained the majority of the representatives from Westminster Parliament to move to Oxford, based upon this law-principle. Even though the king himself was high prerogative in principle.
Rutheford asserts, "James I, could not do anything in his oath in England. The parliament's approbation of the battle of Stirling against king James III is set down in the printed acts, because he had not the consent of the states."