I am afraid Gemini's version is not really very "deep" - it surfaces a lot of information, but on a quite superficial level. OAIs version seems to make that one step forward to proper depth.

We found in our experience it is pretty hard to force LLM to do something in proper depth, and OAI's deep research definitely feels like one of the first examples from big labs on how this can be done. What we typically see is that it is not even the "agent" part that is hard to do, but how to force model to not "forget" to go deep...