When someone says "work on" I think of repair and maintenance. It would be harder to find a semi-auto rifle that is easier to maintain and work on than an AK.
In a way, when you get into building/rebuilding, the AR distorts the whole playing field. It isn't really "built" so much as assembled, to a level that I really can't recall any other rifles reaching. Now folks are used to that as "building" a gun and it makes every other type of firearm seem so difficult to "work on" in comparison.
As for building and rebuilding, I don't think the AK is very difficult AT ALL to build. I still have one that I built on my garage floor with almost no tools more complicated than a hammer, and at the time I built that one, I'd never owned one or even SHOT one. Works fine!
To the real weaponeer types who build FALs, CEMTE/G3s, AR-180s, AR70s, M1919s, MG42s and on and on, an AK is quite literally gun building 1st grade. Assembling an AR-15 is more like pre-Kindergarten.