This is not a simple concept. Here's an example of how this system breaks down. For instance, in the United States, the Black population has a big problem because the Republicans actively attack their community which means they stick to the Democrats reliably. However, because they can't switch their votes, the Democrats ignore them. Notice that this explains the predicament of the Black community without reference to individual political personalities.
On the other side of the coin, the NRA manages to control the fealty of Republican politicians because it has major influence over voters.
https://www.nytimes.com/2018/02/24/us/politics/nra-gun-contr...
The politicians line up even in the face of screaming children whose friends have been murdered. That's a tough job. That must mean there are substantial incentives for them to do so.
In summary, if you rotate the politicians in the manner you suggested, you actually give the corrupting elements more power rather than less.
EDIT: I would be negligent to say that the Democrats merely ignore the black community. e.g. Hilary Clinton's "superpredator" comments in the 1990's that backed the crime bill that vastly inflated the prison population.
On the other side of the coin, imagine a Trump in his second term. If he seems to be acting against his base now, wait until he is free of electoral pressure.
EDIT: While he is acting against some elements of his base (e.g. the tax bill), Trump is making at least some evangelicals who can live with his public persona very happy: https://www.nytimes.com/2018/02/24/opinion/sunday/donald-tru...
While Xi is certainly acting in his own interest to remove term limits, term limits are a profoundly anti-democratic idea. A politician that is in their final term cannot be pressured by the prospect of an election which is a, if not the, primary mechanism of democracy.
Term limits were only instituted in the United States after FDR terrified the business community by extracting taxes from the wealthy order of over 90%. This was promptly followed by the red scare as the business community fought back to destroy FDR's coalition of progressives, unions, socialists, and communists after he died. One thing they did was impose term limits to reduce electoral pressure on the sitting president by 50%.
Note that, on its face, Xi's plan is the opposite of a lifetime appointment. Lifetime appointments are bad because they reduce electoral pressure by 100%.