No thanks. A massive seven day battery, at roughly 6-7 times the volume of the current battery, would make the phone much larger, heavier, and unwieldy. Most Apple customers would pass on that.
And I'm doing fine with my iPhone 15 PM with respect to performance. Especially shooting videos in Apple ProRes 4K 30/60P in log color encoding.
What's holding you back with the current number of cores? Are you mining bitcoin? Or trying to decode encrypted secret communications from foreign governments?
Most people who have an iPhone already have a desktop Mac, a laptop, and/or a tablet. I can't imagine doing what I do on my Mac and large displays, on my iPhone. What an awful experience that would be.
Apple markets to the masses, not to niches, manufacturing and selling 600,000 iPhones per day.
Creating a new iPhone as you describe, would certainly be easy for Apple. But with increased costs and thus great market pricing, and very low sales volumes, wouldn't make much sense from a business case point of view.