FYI: Steam accounts were hacked (around 10th November)

[LP]

From end to start, the password guessing is in my opinion history already, unless system is built really bad.

...or, unless, that system is being used by users who are humans.

Admins will most likely get big red alarms after 5 wrong password attempts already, and ban the IP.

Sure and prevent all legitimate users from the entire subnet access to the server. Banning IPs is a very bad idea as some ISPs serving thousands of users may have only one public IP. By doing so you've just helped a successful DOS attack, which denied access to many legitimate users.

They can shut it down if they see the attacks continuing on numerous IPs.

...and simplify DOS attacks further to this server: just access this server from multiple IPs and it will automatically shut down, how cool is that!

If i was admin to such cloud server network, i'd use same IP whitelist for each server.

I would consider such server system highly insecure because if you rely on IP address whitelist, you are immediately a candidate for IP spoofing.