The phrase "a highly complex one" is correct and usable in written English.
It can be used to describe something that is very intricate or complicated, often in contexts such as academic writing, technical discussions, or analyses.
Example: "The problem we are facing is a highly complex one that requires careful consideration and expert input."
Alternatives: "a very complicated matter" or "an extremely intricate issue".
The FDM process is highly complex one and hardly any theoretical model exist for the prediction purpose.
Since the number of ExPas grows exponentially with a networks' complexity [ 15], the enumeration of ExPas on the highly complex ones such as E.coli MN and TTN is computationally intractable.
Complex biological systems are characterized by a highly complex output, and one of the first symptoms of disease is decomplexification [ 9, 10].
One can think of the Affordable Care Act as a highly complex patch on the even more complex and fragmented health insurance system.
"This is not a simple logistical effort ― this is a highly complex, sophisticated operation in one of the most difficult terrains on Earth," Salama said.
Think of immersing yourself in the colors and textures of a Van Gogh painting, for example, or the scene as you look out at your garden it would seem that one can be phenomenally conscious of a highly complex set of properties, which one could not even begin to describe or conceptualize in any detail.
Dörnyei (2001) defined motivation as a highly complex and multifaceted issue shaping one of the most crucial human characteristics.
The future develops from a highly complex interplay of varied individual needs on one hand and varying demands of social, economic and political interest groups on the other.
Air Chief Marshal Mark Binskin, chief of the defence force, said the situation in Syria and northern Iraq is "a highly complex operating environment in the Middle East and one that continues to evolve".
Of particular importance was the way these different sets of challenges interact synergistically with one another, creating a highly complex context for the delivery of these services.
