The presence of a free-surface between air and liquid can lead to nonlinear behaviour, even in the absence of fluid inertia. Consequently, multiple distinct flow states may occur under the same driving conditions. A natural question to ask is whether simplified models of the system can capture the correct nonlinear behaviour, compared to the full field equations. For the (canonical) flow of a liquid film on the inner, or outer, surface of a rotating cylinder, we find multiple solutions and other complex behaviours can be accurately described over a wider range of parameters using a simplified model system derived via gradient dynamics rather than strict asymptotic arguments.