The author seems to believe people either mock everything or don't mock anything. Obviously using mocks for all your tests is a very bad idea, but that's not how things are done generally.

Unit tests allow you to validate a unit's behavior very quickly. If your unit test takes more than 1 second to run it is probably a bad unit test (some would argue 1/100 second max so your whole unit test suite can complete in a few seconds). In unit tests you use mocks not only to keep the test hermetic, but also to keep the execution time as low as possible.

Then you should have integration & e2e tests where you want to mock as little as possible, because you want a behavior as close as production as possible. For those you care less about how long they take. That's because you usually don't run those tests at the same stage as unit tests (development vs release qualification).

The author does not make the distinction between different types of testing, the resulting article is of pretty poor quality imho.