I might be wrong, but I think you have misunderstood this, or we've come to wildly different conclusions. My understanding is that they were using a dynamic language without types, and 38% of these bugs would have been prevented if they were using static types. My conclusion is that developers would spend at least 38% less time debugging type issues. This is because code editors (e.g. VS Code) have really good TypeScript support, such as autocomplete, and you get instant feedback if you ever make a mistake.

You seem to have arrived at the opposite conclusion, which is that developers would require the same (or more) effort to prevent and fix these bugs while using TypeScript. I think you've missed the fact that most type issues don't take that much effort in the first place. Once you set up the "guard rails" by making a decision about types (or just assigning a value to a variable), writing the rest of the code is pretty effortless.

I would take it a step further and say that TypeScript development is actually more productive than plain JavaScript. (Again because of the better autocompletion and instant type checking in my editor.) I make far fewer mistakes, but I also write code faster.