I've not read the book and quite honestly know precious little about the event but my understanding of the late republic was a society of extreme patronage, where any "democracy" was performed between factional/oligarchic blocs. When a system of democracy is so abused (for personal/factional interest) and exclusive (in terms of the people empowered to cast their), it would be very hard to differentiate from autocratic rule for the majority of the populace.

So the nutshell argument seems plausible to me, but then I'm just a random captchabot from the intertubez with no deep and contextual understanding of the issue at hand.