well, by getting only rageblade as damage, end game I'm usually doing like 350 damage with auto attacks simply because I get like 80% magic damage out of building so much ap.
shadow only has a .5, cresent is a measly .3 and would be .6 if you were damage (but damage is also much more expensive, so remember that part) but mark does .8 if you get the melee hit in which should be no problem.
spell vamp is so gimped as a passive tbh, much better to make use of the other passive.
Show me the item that gives you 25% more AD.
I mean honestly, for 1k gold you get 25% of what? probably 400 ap. that's so much more beneficial.
you can get twice the ap as damage from ap items, so by that account cresent is just as strong no matter what you build. Building ap makes your auto attacks stronger, not by as much but honestly auto attacking isnt akalis thing anyway aside from the small amounts needed to destroy the opponent.