Except it doesn't work that way. Kroak can kill threats, but not in the first turn, and there are builds that can seriously cripple an army in the first turn and probably go first. A couple of thundertusk with huskard delivers 14 mortal wounds to target/s. In the first turn you'll have the warden and 6 guards dead. The khorne formation with 5-6 skullcannons will shoot at you in their hero phase AND in the shooting phase. Wrath of Khorne Bloodthirster will let a Bloodthirster of Insensate Rage charge in the first turn, delivering up to 15 mortal wounds (average 6-9) to each enemy's unit in an area of 8" (at least with the old GHB, must check if it's still feasible with the same deadly rate) SCE can simply pop from heavens a couple of shooting units, backed up by a Venator, killing Kroak. I could continue. Kroak + balewind + eternal starhost is strong, but can be beaten, so the claim 15-0 may be true, but is far from granted. If your opponents are as good as you claim, then the problem is in the models they have at disposal.