The early reports on the web are that the 10.9.2 update fixes some, but not all, GMail problems, and adds a few new ones.
This article from TidBITS outlines in detail the changes in the program (as documented by this particular author, of course). Notice that "accurate and timely synchronization with GMail accounts" is unfortunately not listed. 😉
I did a quick test this morning, and my results were positive: I found received email to arrive as quickly on 10.9.2 as it does on my 10.8.5 machine. Also tested reading the email on my phone to see if the "unread" status would be updated on my desktop computers. That didn't happen immediately (I'm guessing it happened at the next email check time), but it did update correctly (again, on both OSs). Lastly, I tried to archive the message and that change was reflected almost immediately.
Of course, those are just my results this morning. As we have seen, things vary quite a bit.
Bark.