For some, yes 'mAlts' (new word!) are hard to do, as they can be very confusing to switch between. For some, that is. There are other people that do this very well, and use their characters to fill gaps left empty by lack of 'mood' NPCs. I consider those to be NPCs that are there simply to be threre, rather than give out a quest.
As for using mAlts, you can do it on all but the worst computers. Setting the framerate down quite low, and distance to about what you can see across the plaza will do wonders. If you turn off the sound it will do more. Keep one window open at a time and minimize the others.
I have used three characters at once to entertain people in the bar. One was the barkeep, one was just having a drink at the bar and joking with the barkeep, and the last was drunk and laughing at everyone. There was no deep quest of evil event, just a fun night. Malts can and should be used for this. For leveling? What does it really matter to the rest of us? They are not getting all the good quests, as they are open to everyone. They are not taking all the good items, as anyone can buy anything. They are not even having fun, unless that type of thing is fun to them. You may cry that it is not fair, and they are getting ahead of everyone else, but that point is invalid. This is an RPG. There is not and end, it is not a race. No one can get ahead.
If you want it to be fair to everyone, you would have to wipe the game every Friday, and everyone start over. Now set your computer to run as slow as the worst system running the game. Make sure your sound is turn off. And, oh yes, you can only play as much as the person who has the least amount of time. That sounds more fair and fun, right?
In essence, stop worrying about what other people are doing, as long as it is not greaving you. NO one is 'getting ahead'. Is it against the principals of the game? Yes, but I see being forced to level as against it also. Is it against the principals of your character? No, your character does not know it exists. Play it that way. Multi-leveling will always be a minority, and not worth the time spent trying to stop it. Sure, you can cut out all multi, but you then limit all the good roleplayers who are just trying to make the world a little fuller, both in populous, and in life.
I will continue to use my malts, as I do not have a main character, and never will. And the next time you are in the bar and get a chuckle out of a kran making a joke at the menki bartender's expence, you may tip your hat to multi-clienting.