As I think through this, I agree with others mentioning that "deep agents" still sounds a lot like agents+tools. I guess the takeaway for me is:

1. You need a good LLM for base knowledge.

2. You need a good system prompt to guide/focus the LLM (create an agent).

3. If you need some functionality that doesn't make any decisions, create a tool.

4. If the agent + tools flows get too wily, break it down into smaller domains by spawning sub agents with focused prompts and (less?) tools.