Still thinking about this. The Jedi are taken from their parents as children and raised to not have personal connections, and to believe their philosophy is inherently good. That would be fine if they were a secluded and contemplative order, but they are a militant order that acts as advisors to politicians who appear to be morally, physically and mystically inferior to them. It is hard for me to accept that would not eventually lead to them asserting a lot of power and influence over the people they advise, and trying to guide policy as they saw fit. Guidance which would inevitably lead to problems in governance, because they can have no understanding of the lives of ordinary people, or respect for their frailties. And then the Jedi would blame the failures on the ineptness of the politicians, and the whole thing would spiral until the Jedi concluded that nobody was competent to run things except them.
I also think that upbringing and philosophy, in an order that is out in the world as opposed to being cloistered, would produce an awful lot of closet sith, which would likely accelerate the process.
I dunno, given the elements in play, I just feel like galactic history would have progressed differently. It follows a Roman model, but I think the introduction of Jedi into the mix means the model does not really apply. I think some sort of militant theocratic junta would be more likely to form than a civilian dictatorship.
Also, it is pretty clear that the word "empire" is being used incorrectly. The Republic was also an empire, just like republican Rome was an empire.