I absolutely agree about fixtures-as-arguments thing. Ward does this a lot better, using default values for the fixture factory. There's a long issue on ideas to implement something like that as a pytest plugin (https://github.com/pytest-dev/pytest/issues/3834), but it seems the resulting plugin relies on something of a hack.
Also chiming in to say thanks for the good work! This looks like an amazing release - I practically jumped in excitement when I saw the fish style autocomplete.
My recommendation is to get into the habit using StrictStr, StrictInt and StrictFloat as your choice of types to start off with and use str, int, float etc only when coercion is acceptable.
Coercion is quite powerful and saves me quite a bit of work. I write validation for config files that non programmers create. I would happily avoid explaining the difference between a 1 and a "1" to them whenever I can and let coercion do the work. It reduces the mental load on them too.