Clout and the Legitimacy of Authority

The duke disguised as the friar laments in Act III Scene I that Angelo sentences Claudio to death for something Angelo plans to do himself. "Though an angel on the outward side!/ How may likeness made in crimes/ Make my pratice on the times/ To draw with idle spiders strings/ Most ponderous and substantial things?" says the duke, questioning the utility of a law (the spider's wed) that catches only small flies (according to the footnote) but is ineffectual in preventing more powerful persons from flouting it. The point of Claudio's harsh punishment is to establish that the law will not tolerate lechery, yet the law doesn't stand up to Angelo's clout, or his "unsoiled name" (2.4) as he puts it to Isabella which makes his "false o'erweigh [her] true."
Angelo in this sense is the ultimate Machiavellian, because his reputation of precision and honor shroud his actual hypocrisy. I believe that Shakespeare is using Angelo to illustrate how often the values of truth and justice in human society are measured not by the sincerity of one's heart, but by the clout of one's position in society or one's personal charisma. The title "Measure for Measure" I take to partly mean how differently the sins of Angelo are measured when compared to Claudio on the scales of justice; Justice is not so blind to title and privilege.
The actual duke is a questionable character because he seems so well-meaning to the audience, but it is really he who put everyone in this position in the first place. Shakespeare seems to be using the duke as another example of appearances and titles shrouding duplicity, since the duke is disguised as a friar who is supposed to be humble, helpful, and honest (and seems this way to the other characters in the play), but he is actually the grand manipulator of this scheme. The duke is only seen and treated as a friar because he puts on the habit, yet if he were the duke in their eyes the other characters would act much differently around him.
Shakespeare puts into question the legitimacy of authority in this way. The duke is no longer considered a legitimate authority simply because he puts on a friar's habit; Angelo is considered to have authority because he was rendered it by the duke in his "absence." Angelo's will is NOW what counts as the law in Vienna, but why should his authority be considered legitimate by the people? Is it because he wears a fancy hat? Under the duke's rule, according to Lucio (3.1), the same law that Claudio is to be put to death for was largely considered on a case by case basis (or simply ignored) rather than following its strict letter. Since English common law is based principally in custom rather than in code, why should anyone listen to Angelo's personal vendetta on lechery when it was de-facto tolerated in for such a long time? Clearly Angelo has achieved the political legitimacy to be able to enforce such harsh measures in the context of the play, but I think the point that Shakespeare is trying to make is that Angelo's government should not be considered legitimate because it skews justice and is based on the appearance of virtue rather than the practice of it (the Machiavellian ideal).