Even in the only crosshairbased mmo tera dualboxing is viable. The more dualboxing is working, the more partywise gameplay is included. Because basic functions like in Tera “follow” support party gameplay and dualboxing. Your friend can be short afk and follows you or your box follows you. Even dodging wouldnt be infinite. That means there needs to be some kind of aggro system or whatever because not everyone can dodge infinite. Aggro system supports partywise gameplay again. Dualboxing too. But this is nothing bad and shouldnt be punished. It’s just the decision, do you want a party (MMO/coop) game or a singleplayer game.
If its the singleplayer style, I see no clue why I shouldn’t take a raidboss down alone.
GuildWars2 has that singleplayer gameplay. You can do everything alone. But even there for a “timerecord” gameplay some classes are needed. Even there you could easily box some chars - but due to the lack of partywise system - it is/wasn’t effective. Example: Warriors can throw banners on the ground which give you a 90 second buff. You can just box him. Or another example: You play a Ranger who got a healfield (water) and you box another class who can finish a healcombo for this field much more efficient as the ranger can do. But yeah, it doesnt make lots of sense here because the partygameplay isn’t included in this game. It just makes you a bit more efficient. In GuildWars2 there is no need for being efficient/better than others. You go to a Worldboss. Hit 2x and go afk. Even if you died while being on the toilet you get the full loot for the work of 15 Minutes of others. Here comes the afkboxing. Because being afk with 8-10 instances of the game makes sense in guildwars 2. Thats what you get when you have such kind of gameplaysystem.
There is no perfect system out there. Thats true. But destroying a good system just to prevent multiboxing isn’t a great deal.