For a while everyone was saying sub agents is how you save tokens, use lower quality models with limited context to do simple parts of the job after a smart planning agent has put it all in place. Is that no longer true or is this just the result of sub agent being used at the wrong time?

No, you can definitely configure low cost search and apply subagents. CC and Codex do not. Not sure if this is to improve the reliability of their subagents, or just a play to increase user consumption.