The debate is that I need a PHP Framework/Drupal with the flexibility to add custom features to a potentially large application (web and with an api).

However, with a framework, like Kohana, I see myself tackling and re-inventing the wheel with the simple stuff like account management and cms stuff. Account management and quick data collection, like fast form creation, are tedious in Kohana but appear incredible simple in Drupal. On the other hand, based on my limited Drupal experience, I doubt building rapid custom "features" and allowing users to create "groups" and to manage their own roles within those groups is something Drupal can easily accomplish.

To simplify, is Drupal capable of true Web Applications; where the application is a service and provides custom results to each user? Can it provide a dashboard-like interface for users to change their settings or preferences? Can it aggregate data from particular users to provide better results/info to others?

If so, please point me to some knowledge :-)