The phrase "as the key theme" is correct and usable in written English.
It can be used to indicate the main idea or central topic of a discussion, analysis, or piece of writing.
Example: "In this essay, I will explore the impact of climate change as the key theme affecting global policies."
Alternatives: "as the central theme" or "as the main theme".
This time that same team seemed to have settled on the so-called economic recovery as the key theme.
How Rome has continued to build upon its past, both literally through physical reuse and figuratively through symbolic appropriation, from the time of Pope Martin V through Pope Sixtus V, will thus serve as the key theme of this course.
Additionally, the phyletic patterns of bacterial versions and their relationships in the phylogenetic tree strongly suggest horizontal gene transfer (HGT) as the key theme in their evolution.
With respect to how the informants see their role as mentors in the program, the key theme that emerged in our interview data was providing opportunities for career development—more specifically, training students in lab techniques and giving them experience in designing and executing experiments.
Prosperity remained the key theme, much as it has been since Deng Xiaoping led China out of the Cold War by declaring: "to get rich quick is glorious".
In fact how we look at places has emerged as one of the key themes of the series.
Buddha-nature discourse is widely acknowledged as one of the key themes in the doctrinal aspect of Chinese Buddhism from the earliest times up to the modern debates around "Critical Buddhism". Scholarship has focused mainly on its later manifestations (esp. the Dasheng qixin lun and after), leaving its beginnings relatively understudied.
Whistle-blowing has emerged as one of the key themes in the fallout from the public inquiry into the Stafford Hospital scandal.
Immigration emerged as one of the key themes of the EU referendum campaign, with those who backed a British exit arguing the bloc had allowed uncontrolled numbers of migrants to come to Britain from eastern Europe.
The authors report that patient-centred care was "at the heart of the model", and PCC is highlighted as one of the key themes to emerge from the research.
