To clarify this, note that the extensions are entirely optional, and unlike what you are saying, most do not require any dependencies.

The only two extensions that use dependencies are the one that adds template rendering, and the one that implements secure user sessions.

For templates, you can use Jinja on CPython (where you wouldn't normally have space issues), or the uTemplate library (https://github.com/pfalcon/utemplate) on MicroPython, which is quite small.

For secure sessions, on CPython you have to add PyJWT. On MicroPython you need to add the HMAC and JWT modules from the MicroPython standard library, which are not installed by default. These are also very small.