I find it irony that the person calling 10men lolmode, calling other people bad & acting like he's so good hasn't even down Mimiron yet =) not to mention the hardmode contents. If your tanks and dpsers are so good you should at least killed Yogg if not few hard mode bosses already, shouldn't you?
.... or maybe your tanks just not that good, and Shadow Affinity, as many good SPs will agree, isn't such a worthy talent as you thought.
IST increase your dps by a small margin, true, but so did drums, and look at how many people rolled LW just for drums in SW =) that's what you called min-maxing. Absolutely needed to down a boss? No; Needed for min-maxing? Yes.