I don't know which social media platforms use AWS to any critical extent, but I can't imagine them ejecting a big name like Facebook, Twitter, Snapchat, etc over "finding dozens of posts on the service which it said encouraged violence".
I would be near willing to bet that more of the Capitol Hill events were planned on private Facebook groups, chats, etc than on Parler. Signal is a chat app that is secure and group chats are big in planning... So are they going to ban Signal? Conspiracy theories are rampant on WeChat and even over text messages.
Meanwhile there are lots of private conservative/Republican groups on Facebook no one wants to talk about.