Project management in early stages (I will not promote)

I’m at odds with my cofounder about how to get our product built. I feel that the way larger teams operate, with dedicated sprints and tickets for everything, is overkill when what we really need right now is to build quickly. I feel like if there’s something that doesn’t work well we should just go fix it and trust that it’s being done right. My cofounder believes everything needs to be scoped and planned for ahead of time, with nothing getting pulled into a sprint without it being groomed and backlogged. That’s not to say I’m not in favor of product planning - I definitely am. Product specs help us get on the same page about what the product needs to do, without them we’re just wandering aimlessly. I’m talking about turning those specs into granular tickets and monitoring they all get done. We’re a small team and I’m struggling to understand why we need to slow ourselves down by adding process. For other seed-stage founders, what level of product/project management do you do? Have you found a good balance between process and execution speed? I could be totally wrong, but would be helpful to hear it from this community.