Like Waterfall model, Agile methods are also grouped under "process" umbrella. In fact, Agile methods are much more than this. Waterfall model provides a set of steps and guidelines on how to do software development and it has no impact on what technologies you use, and how you design or architect the software. But, Agile methods in turn has a huge impact on how you design and architect software.
In agile methods, Features are built incrementally in iterations and it is expected that the components are also built incrementally. This in turn forces the designer and architects to make conscious decisions for building modular and cohesive systems. At the same time, the less experienced designers would get entangled in their own web of coupled components and have to struggle to refactor for a longer period of time. They have no escape route !! At the same time, Big Upfront design is not the answer.