They aren't wrong. Apple has nothing to fix and Apple made no problems regarding your particular situation.
It's you and your account only, as you proved when you told that the guest account was ok. You have a lot of useless crap on your account, crap that you chose to install, for some pathetic reason than only you can know (if an user is even a bit informed, said user wouldn't install something like clean my mac. What is your reason for having little snitch?).
Anyway, you have Chrome, use Chrome, but install and update flash? Why? What are you doing? Clearly, there are no reports of Chrome's hardware acceleration provoking issues with Sierra. More than likely the issues happen because of a conflict between Chrome's flash plugin and the plugin you download, or some other extension/crap that you have installed.
I'm sorry if this comes out as a rant, but it's something that is 100% your fault, and your strongest reaction is to b*tch and moan, and blame Apple. Not the devs of some shady apps or chrome extensions, not your lack of knowledge, but Apple. I don't know you (neither would I want to), but one can easily paint a picture with your personality, almost without mistakes.
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Saying that Chrome is bad is as pathetic as saying that iTunes is crap. Both are some of the most used, most loved programs on the planet and deserve a ton of credit. It's pretty obvious who's fault this is.