I don't think that the Soviet Union is a good model for China. The Soviet Union didn't fall because Gorbachev got promoted, he was just the one to pull the trigger. It failed because it couldn't deliver prosperity for its people and couldn't rejuvenate its ideology. It's actually a great thing that "Xi Jinping thought", whatever that may be, is now the new ideology. The ideas keep being adapted to changing times. The Soviets didn't do the same and stuck to their failing economic system. They were also highly dependent on the sale of oil and gas to the West and never managed to become a technological peer to the US. Everybody knew that the system was rotten and something had to be doneI am disappointed, but on the positive side if this power is used well and responsibly, and the leaders new to national power have the wisdom and humility of understanding the bureaucracies that they manage, then it's no big deal in the short term. In the long term, the precedent of stacking the PBSC is very bad for continuity of government. We've seen this before with Leonid Brezhnev's stacking of the Presidium in the USSR and hanging on for 18 years. It was a direct cause of Gorbachev rising. I hope Xi won't become a Brezhnev which leads to a power vacuum if he dies, and then a Gorbachev rises. The temporary risk has reduced, but the long term risk is still there.
And I have to be honest, the #1 danger for China in the long term is not US, Taiwan, Japan, petrodollar, etc because China is, like you said before, kinda too big to fail. China failing will drag the entire world down with it anyhow, and the added strategic deterrent ensures that. The biggest danger for China is a Gorbachev appearing because there wasn't enough time to prescreen all candidates before a strong old leader like Brezhnev bites the dust. The time was now to start preparing for a transition of government yet that did not happen.
And in the worst case, China's history could repeat. Xi goes crazy in old age and launches another cultural revolution. He dies and an old comrade that got purged returns to take over. Li Keqiang is ready to be the new Deng, who was over 70 when Mao died