TLDR/ Bottom Line Up Front: Is the Guarantee clause an attempt to empower the government to protect individual rights by constraining State Governments by the Rule of Law?
This question can be considered an extension of "Leading readings of the Guarantee Clause of the US Constitution." From the accepted answer there, regarding the intention of the Guarantee Clause, the opening premise for this question is that the Federal Government guarantee's to each State a Republican form of Government.
In Federalist 10, Madison details firm, distinctions between the direct pure democracy and a republican form of government. His words greatly favor the later. The be well summarized by "rule of law protecting the rights of the minority by limiting the whims of the majority."
In Federalist 39 Madison further details what is meant by a Republican form of government, during the time of ratification and in the text of the Constitution.
Federalist 43 is the best measure of detailing the Gaurantee Clause itself, to a point. The primary concern mentioned was defending against aristocratic or monarchical incursions into the governments of the states, though there is room to view a concern about departures in the state governments from the republican model embodying a rule of law, due to the intimate nature of the relationship between the State governments and the Federal Governments. There is also some brief details about the Clause from Madison's notes for the day it was introduction, in which the speakers specifically discussed concerns of the sovereign states departing from Republican form of governments. This clause echoed a similar statement from the Articles of Confederation.
From those multiple points, ignoring the jurisprudence that was concerned over the definitions on what a republican form of government was, could the Guarantee Clause be seen as an early effort to enumerate a explicit power for the Federal government to constrain the State from violating the individual rights of the minority by holding to the Rule of Law?
Later, following a Civil War and efforts to firmly codify protections for individual rights, the Fourteenth Amendment was ratified. It provided direct protections for those rights, ensuring Due Process and Equal Protection, with a prohibition against abridging privileges or immunities. The same empowered the Congress to pass legislations to enshrine those protections. Could this be viewed as an attempted to further clarify through codification of Federal power to constrain the States (again, ignore the immediate jurisprudence that sought to limit the 14th through judicial activism).