I don't think it's a "problem" with mypy, I just think it's likely the cause of a lot of the programs that the authors think don't type check.

Though I will say, while most have been fixable in a few minutes, some have been a real chore to fix. Sometimes an innocuous looking error balloons into several hours of reconciling obscure type system behavior errors once you start fixing it. Regardless, it's a small price to pay for proper type checking in Python. I've more than made up the lost time in detecting bugs before they ship.