[Vicious Love]

I like to draw the line thusly:
A thug is simply effective against regular troops, to the point at which it is most efficiently dealt with via unconventional spells/tactics.
An SC, in contrast, is completely immune to regular troops. Barring the 50/100 turn limit, outrageous statistical improbability, or hostile magical intervention, an SC will never, ever, under any circumstances succumb to an army of nationals(excepting sacreds) and/or most low-end summons, no matter that army's size. Ye Olde Selfe Buffing Ghost King and Air Queen are good examples of such a SCs: sending a regular army against them, even one worth thousands of gold, is utterly futile.