I think why ppl say sits are easy is coz all they do are cross-xover-revers cross-shin-head-knee...
you know, the BASICS
does Abdullah do those till now? no, he goes way beyond normal cross combos
All three (or four I should say, coz ground moves is a form of freestyle) are as hard in their own way.
you won't really be a master in any of them unless you dedicate yourself to any of them
like for instance, abdullah is only a master at sits, Skora at Air combos, Magnus at uppers
that shows each of them are as hard as each other coz you have to dedicate yourself to one of them to be a master at one of them
(you get what I mean, my brain is all fuzzy so my english is messed up)
the ultimate best freestyler would dedicate like 3 hours to each of them each day