But that’s added layer and slow, no? Wouldn’t something like Opencode be a better option? You can pick anything out of major providers.

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.