I agree with you, a lot of the process if probably automated.
I tought the same thing so I tryied something more during my Google’s approval process . I decided to ask them to review their decision. I believe that when you do that, a real person is reviewing the app since I had to wait 72h before the answer. I asked them the reason since there are other applications on the store that are using the same images. I knew that it would probably be a negative answer but I was expecting maybe some tips and hints. Obviously I did not received what I was expecting 
. Of course I did not sent them any legal document (Thanks for the fair-use information, I will have to read a little bit on it) at this point since this is not my field of expertise and I did not know what to send them without any answer from Twitch.
Well, you know, for my main problem I think that this is also for the images in my application. Look at the response from google : For example, your app’s store listing images contain several game posters.. In fact I would accept to just remove the screenshots that contains game covers in my summary.
I want to make sure that I have all the information that I need before reposting to google 
But you made me tought. In this situation, do I need to receive an authorization from Twitch or game publishers?
I think that contacting the game company to receive authorization is a good idea but I guess that I will run in problem with all the others that I won’t have?
Also, I read again Twitch’s developer agreement and at the begenning, here’s what it contains :
Apps: are software applications, games, websites, channels, and other digital products that you (a) submit to Twitch for license, sale, distribution, or promotion, and/or (b) which use any Program Materials, together with their enhancements, upgrades, updates, bug fixes, new versions and other modifications and amendments.
Related to this text, where do I “submit” my app?