After having attempted to use basically every piece of Canon glass I own on the Sony, I have found that the IQ is just not where I imagined it would be. However, when I mount the native 55mm, IQ is pretty darn good and I don't believe the lack of performance is any fault of the Canon glass.
There may be a small segment of users out there that have gotten the perfectly crafted adapter that causes only minimal degradation, but my belief is that that segment is truly minority.
Furthermore, simply enabling AF and saying you've accomplished the ability to retain most features is not the same as actually making the lenses anywhere near as usable as in their native mounts. Don't be fooled for one second that you will be able to AF EF lenses on any of the Sony bodies in any real world situation where your subject is not lifeless.
I guess I'm one of the lucky ones, as the Canon lenses I've tried on my a7r and a6000 seem to produce results at least as good as (better, to the extent the extra resolution & dr matter) they do on my Canon bodies (I say "seem to" because I've not done anything resembling a scientific comparison, merely taken shots of similar things in similar conditions). And I'm very pleased with the results I'm getting with most of the old legacy lenses (various brands) I've been using, though with them I have nothing to compare the results to except the photos I've taken using them on my OM-D, where similar adapters are involved.
But you're certainly right about AF - if you need to photograph moving things or use the camera in other situations when you don't have a few seconds to spare, AF with the metabones adapter is, as they readily admit up-front, useless. I don't think anyone claims otherwise. But if you're willing to wait, the AF is, in my experience, accurate and it's nice not to have to worry about AFMA. I tend to think MF is faster, though, and it's partly the opportunity to use old MF lenses easily that makes me a fan of mirrorless cameras, regardless of who makes them (I rather like the process of manually focusing, and good MF lenses are far nicer to use that way than any AF lens I've used). (And when you're photographing static subjects, I'm not even sure that AF, even with native lenses, is much faster, if at all, unless you already have a focus point over the subject - in the time you've moved the focus point to where you want it, you could likely have manually focused too, especially if what you're focusing on is small and located among other things that may distract the camera's AF).
In any event, no, these cameras certainly aren't for everyone....