the reason people can multi-table so much is because you rarely have to do anything. mostly you are just folding until you find hands or positions you want to play from, multi tabling reduces the boredom and stops you from playing in hands you shouldn't. It is not uncommon to go 10-20 hands in a row on a table where all you are doing is folding. multi tabling is not hard.
Yeah sure, you are right and multi-tabling works great if you are a level above your competition. Where multi-tabling falls down though is studying your opponents style and play. Necessary to give you an edge against players who are of a similar skill to you.