You can't assume all people use "decent networks" where there is a hub server. You can't assume that hub servers are stable and reliable. Anyone who hangs round for a while on popular networks notices people who have trouble connecting via hubs or via certain servers.
A server is not up 100%, that's the redundancy built into IRC. Every network has good and bad patches. So a decent size network has some servers which (for you) are more reliable, and others which (for you) are less. If your preferred server goes down, what you want mIRC to do is switch to the one thats next most reliable (for you). Not just to say "well, his #1 server has failed so lets try any others at all, in whatever alphabetic order happens to be". Because those others will include some which are almost as good, and some which are definitely not.
If you happen to be on a network with a reliable capable hub server, then yes, you can let it do the work. But in that case you don't need the "try next in group" option anyway. For you it's pointless. So this is a request for the many people who do need mIRC to auto-try other servers, that it is more thoughtful how it chooses which to try, rather than just cycles mindlessly in whatever alphabetic order happens to be.