My strange observation is that Gemini 2.5 Pro is maybe the best model overall for many use cases, but starting from the first chat. In other words, if it has all the context it needs and produces one output, it's excellent. The longer a chat goes, it gets worse very quickly. Which is strange because it has a much longer context window than other models. I have found a good way to use it is to drop the entire huge context of a while project (200k-ish tokens) into the chat window and ask one well formed question, then kill the chat.