If you’re getting to the point where you’re submitting PRs if you don’t know whether the foundation of the change is flawed, you have more pressing issues than wasting time in code review fixes.

There's only a limited amount of context and decisions that can be effectively communicated informally without looking at the code. Sometimes it is required that people look at the actual suggested implementation, and when doing so they might spot fundamental issues that had not been found beforehand. The conventional format for doing such a review is a PR.