Originally Posted by GUnTI
You are also forgetting that with the nerf to the MS it also gained the passive ability of ignored creep collision which can actually affect your dps. However I will give way that MS of PD was a bit more then I should of made the comment of being too hard to pass up.
On the Pen vs Crit part I have a question. How close to equal is the 50+50% to 34+55%? cause really % does get calculated first however 5% could vary by quite a bit compared to a flat 16 Pen. Also you do bring up a really good point and something I didn't actually know about Hurricane. I wonder if they really wanted Black Cleaver to proc with Hurricane or does it proc with Tiamat passive as well?
Tiamat only works with melee stuff, so Hurricane and Tiamat don't work together at all. Black Cleaver applies mostly because Black Cleaver applies with all physical damage applications, including on-hit effects (were most on-hit effects don't apply on other on-hit effects, for obvious reasons).
For the armor penetration question, 50%+50 would be better than 55%+34, just because 55%+34 is a little lacking in the flat-penetration department. As the % penetrations available exceed 50%, stacking it ends up being more effective the more armor opponents have (which makes sense, considering it's called armor penetration). Once % penetrations exceed 50% the flat penetration really stings though, which is probably the reason Black Cleaver's and The Brutalizer's flat penetrations were nerfed; and in the case of Cleaver turned into a unique passive. But 55%+34 still offers an 80% boost in DPS against 100 armor and gradually scales higher the more armor opponents have. You need 11 flat armor penetration at most to actually double DPS against anything with more than 100 armor as well, which isn't particularly hard to get, at least any more-so than bumping critical strike chance up to 80%.
Just for a quick point of reference, 50%+50 is just the easiest way to represent armor penetration (or magic penetration) for doubling DPS. You can hit that point with varying % and flat values.
For 100 resistances it's 100, for 200 resistances it's 150, for 300 resistances it's 200, for 400 resistances it's 250, for 500 resistances it's 300, for 1000 resistances it's 550.