> If I'm doing something more complex and storied to the point it requires stacks with dependencies, then I'm questioning why I haven't split and chunked the thing into smaller PR's in the first place and having those reviewed.

It looks like you see stack PR as an inherent complex construct, but IMO splitting the implementation into smaller, more digestable and self-contained PRs is what stack PR is about

So if you agree that is a better engineering practice, then jj is only a tool that helps you do that without thinking too much about the tool itself