There is a part of the conversation on gitter channel:

Is there a way to disable content decoding in aiohttp?
Ah, nevermind, I see the auto_decompress parameter for a ClientSession(). It would be great to be able to do this on a per-request basis. Or the ability to get the raw content from any response.

I think #3440 can solve the issue (along with many others).
Stay tuned.