I do not think adding this will help you much, but it may give you some perspective.
After reading your posts in this thread several times to make certain I am not missing anything, the numbers you are reporting are in line with those reported across the broad range of digital cameras by various manufacturers. Nikon, Canon, Sony, Leica, Fujifilm, etc. Use your favorite search engine to lookup (brand) af keeper rate. People are reporting af keeper rates now in the high ninety range. You will find page after page of tips and technique improvements for improving the keeper rate. As well as page after page from the manufacturers touting their new camera models with improved af keeper rates. af is vastly improved, but it still is not perfect.
It maybe that there is something slightly wrong with either your camera body or the lens, but I suspect that if you send it in to get it checked, it probably will be okay. Getting a new XH2 will make your camera dealer happy and it is a fantastic camera, but, …, getting it solely in hopes of better keeper rates is probably wishful hoping.
For what it worth, (more of what you probably do not want to hear) back in the film days, a af keeper rate over 50% was considered great. Those expensive film rolls certainly did not hold the thousands of shots memory cards hold.
I very well understand the thought of maybe missing that one shot, try when possible to push the shutter button several times, those cards hold a lot of shots and it is easy to delete the extras.
I hope you get this resolved in a way you like.