The idea of systems and thinking systematically, about the properties of the whole being different from the parts and the dependency on interaction between system elements has been around for a long time
Like most things we could trace it back to the Greeks and atomistic theories of systems
General Systems theory traces back to the start of the twentieth century
The pioneering work of Prigogine and others which gives us complexity theory happens in the middle of that century
Then, in the latter part of the Century those aspects of systems theory which had build cybernetics and modelling starting to enter the popular space with Business Process Re-engineering at the hard end and Learning Organisation at the soft
It was a characteristic of that period of development that the complexity of system would be resolved by engineering design, often bottom up, or definition of specific outcomes
Zero based budgeting was around then and evolutionary approaches to organisational design which had been the de facto state were replaced with end point determined models that were then implemented
Complexity science has a different origin and history from systems thinking
I have never disputed that the various forms of systems thinking have sought to address complex problems, and in doing so have developed a body of methods and tools of considerable utility
Trying to avoid differences or minimise them will actually increase progress, inhibit conflict and not reduce it