I doubt they meant to imply previous leaders were unstable. Stability is good for investment, and the current government is stable. A new leader could be any of the kinds of leader that make investors look elsewhere.
How can you have stability when you're at the whims of a dictator. Having a dictator is quite different from a single-party rule that changes its leaders.
- The risk that a stable leader with increasingly unlimited power will lead to stagnation, deep corruption, or war.
- The risk that a disruptive leader emerges after Xi and is not countered in time by government mechanisms (e.g. internal elections within the party).
Historic consensus seems to be that the former is the bigger danger, which is why even the CCP previously put a limit on presidential terms.