Full-range leadership that consists of Transactional, Transformational, and Passive-avoidant/Laissez-faire is referring as a leadership style or leadership theory?
The Full Range Leadership Model of Avolio and Bass shines a light on the ability and behavior of leaders in different work situations from the perspective of three leadership styles, viz., transformational leadership, transactional leadership, and passive–avoidant or laissez-faire behaviors. The model is a trait-based approach to certain styles of leadership, of which there are several others, and falls short of theory. (A theory is a well-substantiated explanation of an aspect of the natural world that incorporates laws, hypotheses, and facts.)
Article The Full Range Leadership Model: Essentials and Practicum
Presentation Reflections on a Multifactor Leadership Questionnaire 360 Le...
It is actually a question of definition. Olivier Serrat gives a good explanation based on the work and definitions he cites.
In our model, we use different words. We take people on a journey of development towards Transpersonal Leadership (which is about transformation of oneself - beyond the ego) and which incorporate 6 emotional intelligence leadership styles developed from the original research of Goleman, Boyatzis and McKee. As Tolstoy wrote in War and Peace , "Everyone wants to change the world, but no-one wants to change themselves" - this where the dilemma continues to be. See my research lab and in particular our acclaimed book "Leading Beyond the Ego: How to Become a Transpersonal Leader".
This is depending to whom you address the question. Usually, students don't like to learn theories, that's why I like to tell them about leadership styles. But both classifications are correct, depending on the context.
The full Range of Leadership Model is a general leadership theory focusing on the behavior of leaders toward the workforce in different work situations. The FRLM relates transactional and transformational leadership styles with laissez-faire leadership styles.
The question can exhaust an array of opinions and depending on whom you ask, the answers will vary. As a DBA student, I feel Full-range Leadership conceptualizes the behaviors, personalities, and traits of specific leadership styles and I specifically view it more as a theory.