I've never seen any such performance issues. In my testing worker mode has always been at least as fast as DOM mode. In some cases it's much faster, especially if it has to do significant main thread work, as described in the blog post. It's also been the default for over 6 months now and I've never heard of any other such complaints specific to worker mode, so as far as I can tell all the evidence is it works fine for the vast majority of users.
If you have serious performance issues I'd advise filing an issue at crbug.com with details about the device so Google can look in to it. I can't think of any reason at all there would be any serious performance reduction in worker mode. As the blog post describes, it should be better and smoother, since there is less chance the browser can interrupt it.
Fullscreen mode only working on HTTPS is nothing to do with worker mode. Many browser features require secure hosting now, including fullscreen mode, regardless of worker mode.