Testing is more expensive up front and in maintenance than type annotations. A test suite comprehensive enough to replace type annotations would have an ass load of assertions that just asserted variable type; if you were involved in early pre-TS Node, you remember those test suites and how they basically made code immutable.
> (2) it regularly missed deeper problems
This is a skill issue. If your types do not match runtime behavior and you choose to blame the programming language rather than your usage of it, that's on you. There are a lot of unsafe edges to TS, but a diligent and disciplined engineer can keep them isolated and wrapped in safe blocks. Turn off `any`, turn on all the maximal strictness checks, and see if your code still passes, because if what you said about infinite scroll is true, it won't.
