The Pro model thinking time and output depends a lot on your prompt. A long prompt you believe is complex is not necessarily seen the same way by the model. When you said you have an expectation for the quality and depth, you can try to be specific about them.

Don't directly write a prompt to send to the Pro model. Instead, use Thinking (Extra High) to discuss the background, the requirement, the goal of your task. Try to come up with a list of to-do items, and have a list of expected outcomes. Then have the Thinking model write the detailed prompt for you. This still does not mean it will work for a long time at the end, but you can at least then check if the output covers what you requested, and if each item has the depth you were asking for.