Sometimes, a simple conversation with a small group of people to thrash out ideas and develop solutions into concepts is a more effective approach than brainstorming or other structured ideation events.
Does this mean you should stop brainstorms in favour of conceptual conversations? Not at all. Conceptual conversations are better when you need to develop solutions or need to solve complex problems.
Brainstorming and crowdsourcing are better suited when you need a number of ideas, most likely incremental improvement ideas. For example, if you are looking for product improvement ideas, you probably do not want a single concept but rather a number of suggestions which can be implemented.