there is nothing wrong with the 50L.
it's a people lens. it's plenty sharp.
it's f/1.2 - so if you're not nailing focus, you need to work on your technique.
Can't tell if you're being sarcastic or not...
Exactly. It's not the f/1.2 aperture that causes the focus problems on this particular lens. It's actually the field of curvature and is especially prominent at close distances from about f/2.8 to f/4.5. The lens will back-focus and there is pretty much nothing you can do about it. I thought it was pretty underwhelming for $1699.
You could manually focus... but I think the presumption is that those who struggle with f1.2 are using bad technique, like focus and recompose... which will all but guarantee the subject is out of focus.