Well, that's the point; for most people the existence isn't miserable. Certainly not suicidally miserable.
Now that's exaggeration. But even dealing with your first point, it isn't one of extreme control. Commoners go about their everyday lives without even noticing the difference; they have to step lightly around the nobles, but that's always been the case. The only real difference is that they'll bow lower.

Perhaps you refer to the Seekers/Listeners when you say this, but really any modern civilian police force looks positively totalitarian compared to the most intricate of premodern secret polices. DNA fingerprinting? Chemical analysis? Photography? Yes, the Seekers might be advanced by the standards of the bumbling town guards in most places, but they're by no means as controlling as the KGB, or the Gestapo, or the CIA, or any number of agencies today that can record every word written or spoken that's sent over a communications network.
The form of slavery they have does not seem to be overly confining. This is not the brutal American chattel slavery, but a pseudo-Ottoman style that doesn't seem to be much more restraining on social mobility than the political systems in most of Randland. Andor is an exception, certainly, and possibly the Borderlands, but we're getting a skewed perspective because our POVs are mostly those of a) heroes, who get an exemption for being ta'veren or b) Aes Sedai, who are rigidly egalitarian, at least with respect to non-Aes Sedai. The clues are there in certain passages. So, I don't disagree that the Seanchan social order is due to be shaken up, although its meritocratic aspects might moderate the degree of upheaval, but the entire world as we know it is due for the same thing. I wouldn't want to be a Tairen High Lord once every peasant can put his hands on a flintlock rifle.

As for backstabbing in upper government, it's all-pervasive. In Cairhien. In Tear. In Andor. In Tarabon. In Arad Doman. Among the Shaido. In Altara before the Seanchan. Even among the Malkieri diaspora; in New Spring Lan frickin' Mandragoran was worrying Edeyn might have him assassinated. Literally every national government of which we've seen any degree of the workings has been consumed with backstabbing, distrust, and extreme self-interest in the higher ranks.