Most new players are caught out with a lack of knowledge of how busy realms are, which ones have the high populations, which ones are Horde/Alliance. Although it’s been simplified a lot with the removal of PvP realms there have been plenty caught out by the different server types in the past too.
If they are not joining a friend it’s very hard to know what to choose. It’s even harder with the loss of many of the sites that used to track that info after the API changes made by Blizzard.
A balance indicator would probably be a nice addition to the realm list. I’m not sure how they would measure it, there would need to be clarification. Whether it’s based on the characters on that realm or those active at the time. Either way it would be better than what we have now.