By contrast, does anybody think that having "stronger" dynamic typing (don't convert strings to numbers as implicitly, etc.) like Python's would not be a huge benefit?
That's actually one reason why I often opt for TS. While the 'stronger dynamic typing' isn't the most sexy benefit, it has saved my ass quite often.
There are so many situations where my input is strings (JSON through various API's) that should get turned into just integers, floats or (string) constants shortly after being consumed. Using TS types from this point onward promotes discipline to do so on my part, removes any ambiguity going forward, and alerts me if I treat these values as strings or any other wrong type (which commonly happens to me, at least, when using vanilla js).
I agree - one thing is noticing bugs, which is easier with stronger dynamic types.
And as you say it's also important to setup some boundaries so that bad values can't travel to the other end of the program before you notice, which is a pain to debug.
I like to make value checks on module boundaries, but do much fewer checks inside modules. I typically do this using assertions. Optional types can be a way to do it with less noise. But they still can't replace asserting arbitrary invariants, like invariants involving multiple values.
