> I've had it turned on for a while in a large web project and it's been very helpful, and almost feels type-safe again

In my experience "almost" is doing a lot of heavy lifting here. Typing in python certainly helps, but you can never quite trust it (or that the checker detects things correctly). And you can't trust that another developer didn't just write `dict` instead of `dict[int, string]` somewhere, which thus defaults to Any for both key and value. And that will type check (at least with mypy) and now you lost safety.

Using a statically typed language like C++ is way better, and moving to a language with an advanced type system like that of Rust is yet another massive improvement.

Yeah, if you're going to use static type checks, which you should, you really want to run the checker in strict mode to catch oversights such as generic container types without a qualifier.

Although I've found that much of the pain of static type checks in Python is really that a lot of popular modules expose incorrect type hints that need to be worked around, which really isn't a pleasant way to spend one's finite time on Earth.