I am a strong believer that every developer on a team should know how the code works. Emphasis on HOW. You only know that if you go to the source of truth. That is how people become proficient with a skill — by doing and re-doing and re-doing things.
I disagree that it's wasted time. The time spent investigating how a piece of code works is time extremely well spent.
If the code is too difficult to understand — of course one can hind behind types.
So, yeah, to sum it up — I think types are an overhead for a well written piece of code.
If the codebase is small and owned by a few people then it might be true. But when the codebase gets large enough and worked on by multiple teams - it is unreasonable to expect that everyone will understand the workings of the whole application.