The comment was about code working when you first run it--not exactly where input outside your control comes in. Also, you'd be surprised how much types can catch, but feel free to completely ignore my opinion if that suits you ¯\_(ツ)_/¯
Both give you super fast feedback and a lot of issues can be solved before you finally launch your software for the first time. But neither will save you from bad design or misunderstanding your requirements.