1) Only allow people to friend request people once they join a GC or only other non-GC players. This doesn't mean the non-GC people can't have a friend list, it just means that I'd have to friend request you. This is a bit extreme but at least when RMTs get banned, they actually lost something. A throw away lvl 1 account doesnt mean much. A lvl 22-25 account that had to be ifrit.

2) Allow a setting that decides what level player you want to be able to send you /t. So instead of having a blanketed system of a number, let us choose. The command can be simple. Like a do not disturb but it only apples to certain lvls. It would be like /dnd 1-30. So that means anyone above 30 can message you. Also anyone who is in that lvl gap would see the dnd symbol next to a character but anyone who isnt in that gap wont.