I'd say don't give up hope yet & ask if you clear the Flash-specific cache. I predominantly play on a Chromebook (which isn't well known for high end processors & the like) while using a router that isn't the best & a cable internet connection that's "only" 10-12 Mbps (compared to many whom I speak to that are 16+ and the high end connections of 50+).
By simply clearing the Flash cache of everything except the WGT stored item, I can play with barely any meter issues. Sometimes the best I can do is come in right around the ding rather than hitting it consistently. However, there are no instances of "rocket meter" nor is the meter terribly jumpy. Just an occasional small hitch, which may leave me with a 40 foot putt at worst (instead of a wretched swing and a lost ball).
I'm not calling in to question whether you've upgraded all you can & tried every fix. Maybe there are specific issues you face that I haven't. The advantage of a Chromebook is there is little running in the background, that's for sure. I'd say try clearing your Flash-specific cache (usually the general cache effects me very little) of everything except media.wgt.com, I believe it is. Only delete that item after updates, if any issues appear after an update. I'm sure there are others who may be able to contribute more, especially when it comes to browsers (given that I'm using a Chromebook, it's Chrome or nothing for me!).
Best of luck pal.