what version of the API are you using? Can you try the latest? I don't know any issues with comtypes and the API.
You might want to try our pre-release of the Hyper API (the successor of the Extract API).
With the all-new Hyper API, Developers can now utilize full CRUD support at Hyper-speed and unleash the power of SQL to interact with .hyper files.
To get access to the pre-release, you need to join the Tableau Develop Program. If you are not part of the Developer Program yet, register here and join the “Developer Program Sprint Demos!” under “AVAILABLE OPPORTUNITIES”. Then, go here for more information on Hyper API features, supported languages and platforms.