I think testing as a cost and manual QA has another cost. Depending on the cost over time (maintenance or manual QA) and the upfront cost, as well as the risk of refactors, which needs tests, there are moments where one option is better than the other.
It changes, so it is worth considering.
I dont think they replace each other, they are complementary - they do overlap though, which is why people think you can trade them off - a test is not creative, a human is not an automaton.
We have been using humans for automations for a long time, factories have been a thing for quite a while now.
They have an intersection, the fact is that you might need only the benefits in the intersection, not all the benefits. Given that, it could make sense.
I have way more fun writing tests, but automating certain things have a steep maintenence cost, a checklist for humans is a better idea in that case
