for any hybrid character, i have experienced that for the specific type of utility you are using your character for, the type of runes that you choose to use more or less dictates how your character is to act (and build) in the battlefield.
my sion rune page uses atk speed, dodge, mana regen and armpen build:
15gold change in pocket:long sword+health pot
900-1200:boots into anti general damage output be it merc treads or dodge boots
1200:zeal 300:elxir of fortitude
1850-2200:bf sword or phantom dancer
2200:"" or "" (ideally you just farmed 6450 here and about 7000 altogether)
800:the black cleaver 9 if game doesnt end spec for doing damage within the current meta
your build differs from mine in the fact that you are building survival items mid game along with your dps. it intrigues me to know that the cost of your items relys heavily on your ganking ability with sion, which is a good thing, i think he is a strong ganker. which is why i mostly farm(and help ganks) for bf sword mid-game. my build greatly benefits from attack speed runes allowing him to hit 1.0as really early. i try to make up for what he lacks for survivability and lasting mana pool. your build i would assume straight armpen and something else giving you the ability to do as much dps as possible, with the statement
"with this build i am able to kill any none tank with ease and any tank with my ult
i crit for around 600-1000 on none tanks and 300 on tanks "
i will test more of this when i build a stronger rune page.
i think your choice in going all out arm pen runes is vicious for sion, because he can hack through all that mitigation and your mastery page is identical to mine, although sometimes if i play draft ill put the 9 other ranks into defense focusing on the movement speed benefit thing. your sion hits a little harder than mine because you choose to go long swdx2 earlymid game. i honestly think the vampire scepter is negligible, but i will have to test it now after seeing your build.
all in all though your build interests me (aka. i like it) and i will try it out next chance i get to play.