Great point, I've found Sonnet really can't be beat on many tasks, but increasingly finding Gemini-Pro and o3 handle the tough bugs and refactors best.
I haven't tried opencode, but I am very happy with claude code overall, and most of what I do is with opus. When I'm using zen to route to o3/gemini it's usually for a more difficult task that I don't mind taking longer anyway - I'm usually telling it to get solutions from both o3 and gemini pro and then to use o3 to evaluate which is better. I don't think the added layer of claude choosing to use the tools is really adding much here, claude picking tools is a lot faster than o3 writing code.
That's why I've been using agro to launch agents from each of the main LLM vendors and checking their results when I'm stuck: https://github.com/sutt/agro/blob/master/docs/index.md