For example, one of my main uses of multiple-profiles is that I have a different profile for every proxy I use. I can launch a firefox profile that's proxied side-by-side with my usual firefox (aside, the firefox proxy settings are exposed via the UI, unlike chrome).
Chrome, I'd have to run "google-chrome-stable --proxy-server=$proxy" and then, again unless I'm mistaken, all accounts will use that proxy server. That, by itself, is a deal breaker.
I'm not familiar enough with chrome's settings and so on to say what does and doesn't leak; I could be completely wrong on all of this, but I suspect I'm correct.
Edit: On looking more, Chrome's does look more complete than I thought. The proxy bit still is a dealbreaker for me (well, and I'm adverse to logging into a google account), but I retract much of what I said.