LOL, so many people complaining about the "useless" or "wrong" procedure of the OP. Obviosly, they need to re-read the post(tbh, is too long and maybe not too much clear but the logic is correct).
About the item drops: i've been thinking for a long time about this and the only conclusion i have is that, yes, drop is "random"(doesn't exist an algorythm that can output a true random number). The only way i can think about to maximize probability for drop is to have a clan full of friends who all leave the eb(clan) when the eb is at, let's say 1%, except the one who's hunting the item(obviosly he must be the one who start the eb). But i never tested this and after many,many,many,many destroyer,CoR and now ACC i'm still a noob without chest. Now doing b2b ACC, at least it pays well