I think term limits are a weak defence against autocratic leaders, because in such situations the separation of powers necessary to maintain the constitutional

I think term limits are a weak defence against autocratic leaders, because in such situations the separation of powers necessary to maintain the constitutional check usually doesn't exist. I.e. there's no independent judiciary or opposition bloc in the legislature. In a system like China, these institutions are politically inert facades, designed to outwardly resemble their democratic counterparts, but with actual power remaining wholly invested in the executive, which is wholly controlled by the ruling party. The real checks on an autocratic leader are rivalries within the ruling party's elite, and once a leader like Xi has achieved dominance there, then amending the constitution to remove the term limit clause is trivial.