I see Messaging as a broader element and which can be broken down into:
- Corporate / Brand messaging
- Segment messaging
- Solution or Product Messaging
As for Pitch and Story, I agree that your pitch may include your story however I typically see the "pitch" as your typical sales pitch. I once heard of a good framework: 30-3-30. The 30-seconds pitch (or elevator pitch), the 3 minutes pitch (typically quick overview after someone says 'tell me more'), and your 30-minutes presentation. This last one is where you weave in the 'why change', 'why now', and 'why you' story.