Servers don't disconnect you based on how much information they send to you, they disconnect you based on how much you send to them (if you ignore SendQ which I've only ever seen surpassed through /LIST). Sending 5 /who #channel commands in 3 seconds is still only equivalent to sending 5 commands to the server in 3 seconds.. if you think about it, it's not much. I'ved typed faster than that without problems.
What the server sends back is not part of what can flood you off, otherwise PRIVMSG floods would make it extremely easy to disconnect any user. The server will, however, throttle your connection and probably lag you a bit, but you can always put your /who commands in separate timer events to compensate for lag if you join multiple channels on connect. One single who command is unlikely to lag you let alone drop your connection even if the channel had > 300 users in it. I've never seen that happen. You're probably referring to sending multiple who commands successively for large channels, which is your fault as the scripter.
