“the regime can defend itself from internal threats by launching nukes”
Will they nuke their own cities, like a rebellious Hong Kong? No.
Would mobs raging against a domestic economic crisis believe, or even care about, Government rhetoric about foreign war? Not if economic conditions get bad enough.
Would the regime survive a nuclear exchange? Doubtful.
Limited, sure - but it can apply. Ask Gaddhadi. Foreign influence is often a factor in regime change.
Also consider the huge spy apparatus China has. Quite extraordinary!
It’s important to study history because people don’t change.
However the circumstances they act in can.
Feudal systems with modern defenses are not changed as easily as before.