Can anyone explain to me why the Plan subagent is a good idea?

I just went back and forth for a long time refining an idea with CC opus 4.5. Got to a place where we were seeing "eye-to-eye". Put it in plan mode and asked it to make a plan. It immediately launched a sonnet 4.5 "Plan subagent". This feels wrong on 2 levels. 1) the plan is the most important part why delegate to an inferior model? 2) the Plan subagent doesn't have the context of our whole "eye-to-eye" conversation, it only has a brief "handoff" when it is called, that doesn't have the nuance and depth of our whole conversation.

I really wish there was an option to disable the Plan subagent. BTW, mine is set to "inherit" so that inherits the model setting, nonetheless, my plan subagent was sonnet, not opus.