To be honest, having lower-level friends teleport to you in more difficult worlds like DS and CL ruins our sense of accomplishment. We worked hard to unlock all the worlds, and get our Grandmaster gear, etc. But then you have the "Magus Wizard" who ports into our battle, drags in another enemy, then promplty gets defeated on the next round. Or they inadvertedly summon that Gurtok in the Plaza of Conquests and they are reluctant to leave. So we are forced to leave our hard-earned quests and boss fights to help someone who has yet to complete 2 more worlds before they see these enemies. So I'd like to propose a "level minimum" to each world (preferably the average level one would unlock that world).
This topic has been covered numerous times including a Feedback Friday. The best advice I can give is turn your port option off. (It can be accessed quickly by hitting escape.) Tell your friends not to port without asking first (if you leave ports on) and removing those that don't comply.
KI has allowed porting to all areas to those who buy areas with crowns or subscribers. They don't seem inclined to do level caps. So we need to manage our friends porting to us by ourselves.