This may be an unpopular opinion here but if the TorBrowser folks cared about security they should switch to a Chromium based browser. The sandbox provided by it would be robust and well tested as it's used in Chrome.
I don't see why the two objectives of having a secure browser and the privacy/anonymity provided by Tor have to be diametrically opposed. You can have both.
Because removing all of the Google-related features from Chromium would be a very large task indeed. Quite a few people have discussed it within Tor (and IIRC some people started working on it) but it might not be as good of an idea as you might initially think.