My bigger priority has been moving from Mako to Jinja2, especially for some particularly horrid templates that could not be highlighted or formatted because there's not many good Mako tools, JSON schema validation, but I definitely agree type annotations are critical.
VS Code is smart enough to catch a lot of stuff sans annotations though, so you can get by with a lot of nonsense, especially when half your time is just fighting GStreamer and you're not paying as much attention to the python side.
There's nothing better than GST that I've ever seen for dealing with media without actually having to touch the performance critical stuff in your own code, but it is not easy to debug stuff buried in autogenerated python bindings to C code, especially with an extra RPC layer to use a background process and defend against segfaults.