If Bob the nuclear engineer does something fucking stupid, but there’s an automated failsafe that resolves the problem… was there really that big of a problem?

Sure. The idea is plausible. They have tried such strategies, and improved them for several decades, and they seriously believed that all would be good enough. But Chernobyl and Fukushima have taught us that it is not possible to do it without super terrible accidents that cost simply too much (money, lives, health etc). So, we know now that mankind is not able.