> China is led by a fairly Leninist party structure in nominal terms
China's party structure was fine and decidedly non-dictatorial. Deng was not a dictator and neither was Hu Jintao. They did not, like Xi has, ensconce themselves as leaders for life [1].
Nothing much about the party structure has changed. Xi doesn't get any more power than he has right now simply because of a term limit removal. Given how opaque and complex the power distribution inside the communist party is, Xi could have feasibly governed with a marionette in place without changing the term limits at all, just like Putin in Russia while Medvedev was in office.
China was certainly much more dictatorial than any Western country before this change, and it isn't much more dictatorial now. Xi's extension of time in office isn't really related to governance as much as it is related to the problem of succession. With significant amounts of the old guard finally reaching retirement age, there is a fear of political instability in the party.
Xi doesn’t have more power because of the term limits removal. But the fact that he was able to get the term limits removed was a public display of the power he has accumulated.
And the way he has done that is by imprisoning and killing competitors to his power. The fact that he could even contemplate bringing the term limit up indicated that he was certain at that point that there was no one to compete with him within the party, who would protest the term limits removal.
China was certainly much more dictatorial than any Western country before this change, and it isn't much more dictatorial now. Xi's extension of time in office isn't really related to governance as much as it is related to the problem of succession. With significant amounts of the old guard finally reaching retirement age, there is a fear of political instability in the party.