I don't think it's a fair read to say that the Jedi supported an ineffectual Republic, it worked very well for a very long time. Nobody is going to make a movie called Star Wars Peace, so we only see the fall, and no government looks good when it's being actively demolished. But both the OT and the PT repeatedly inform us that the Republic worked pretty well for a long time.

Supporting a violent rebellion is only wrong if violence is an utterly unacceptable tool and/or the system being rebelled against is legitimate. Since no government declares itself illegitimate, the fact that the Empire says it is illegitimate is information-free - there's no chance of them saying otherwise, it is up to the moral discernment of the characters/audience to decide whether rebellion is acceptable. Since we, the audience, are going to see a fun action adventure about how cool space battles are, we're kinda already answered this one.

The freedom/totalitarian axis is more subtle. We tend to think of freedom as freedom to do what we want. The freedom pursued by the Jedi is freedom from want, applied equally to all beings. As the other side of that coin, the totalitarianism of the Sith is the logical and inevitable endpoint of pursuing what you want, unchecked by such constraints as the rights or desires or freedom of others. Anakin's fall is a perfect example of this, he doesn't want Padme to die, so he butchers children because he thinks that will let him save her. This not only disregards the children, it robs Padme of freedom over her own life; given what we know of her as a character would she have wanted children murdered in her name? Of course not, but Anakin, enslaved by his attachment and the fear that comes from that, no longer has the compassion to allow anybody else personhood. Indeed when Padme objects to what he has done, Anakin tries to kill her, because she has now become a threat to his attachment to his self image as heroic savior and liberator.

The element of Revenge of the Sith that is profoundly weird by most modern blockbuster standards is that the hero getting ultimate power to obtain everything he wants, free of limitation from others, is a bad thing. Having taken great power, the protagonist creates not justice but oppression. His willingness to do anything to save his loved ones is not strength and truimph but profound weakness and failure. Normally special magic chosen one movies, particularly in the age of Marvel, tell us pretty much exactly the opposite of this, if only the special people (meaning the audience surrogates) had ultimate power they could fix things, that anything done to save friends and family is not only justified but heroic because friends and family are ultimately all that matters. Often said in exactly those words.

As for slavery still existing, one can be good and neither omnipotent nor perfect.