I just did a comparison between the number of clicks it takes to connect to a network using a new window with mIRC 6.21 and with 6.2
There is a larger number of clicks required. A count of two (2).
Personally I don't find that to be too big of a deal, and if you connect to the same network(s) all the time, you could easily script up your connections so that they go automatically when you start mIRC. Could be done with as little as one click, depending on how your system is configured.
The part that, appears to be missing, is the Connect To option in the Server selection dialog.