E2E is not a replacement for unit tests. E2E tests are more difficult to write, as they can require a lot of setup to get all the exact scenario needed for each piece of functionality we need to test, they tend to be flaky, they can be very slow, etc.

The purpose of unit testing is to isolate the various scenarios by making sure that each unit/component/whatever correctly responds to its various inputs. In this way, we only need to set up the relevant scenario for that unit. If we tested each of these piece of functionality in an E2E test, then each test would also need to set up the user session, settings, etc. It would be a nightmare to author and maintain, compared to the simple, straight forward unit tests.

In contrast, E2E tests are good at making sure that the whole system works well together, and that each unit is getting inputs and providing outputs, and that the page doesn't break in the process. Both are needed to maintain confidence, and each solves a different problem.