They're referring to application performance, specifically UI, not network latency.
Correct. I gave up trying to figure it out, wiped my settings, redownloaded TorBrowser and it is fine now, even after reinstalling my add-ons.
Too late to edit but I agree with the other poster about not installing add-ons, if you're serious about privacy. However I just use TorBroswer as a quick proxy to bypass my network's blacklists.