So...I've been stomping on things quite a bit since my Wraith Knights got promoted to Gargantuan Creature status. Having sixed-out a number of models (including a pair of Bloodthirsters last night) with Stomp, I've arrived at the conclusion that Stomp, as written, is dumb. Here are my proposals:
1) Stomp occurs at Initiative Step Zero.
2) In addition to not being able to Stomp Super Heavy Vehicles and Gargantuan Creatures, Monstrous Creatures cannot be Stomped.
Why? Because unlike Melee D or Ranged D, I don't have to roll to hit, I just have to roll a die and get a '6'. Hardly 'interactive' (and that's a buzzword these days, isn't it?). Also, if you survive my I5 or I4 attacks, you should get to swing some hammers (or power fists or D-axes). If I survive your I1 attacks, I have 'earned' the right to stomp you, contemptuously, into oblivion. Monstrous Creatures are essentially all that are available (melee-wise) to 'Nids and Daemons to try and engage Imperial and Wraith Knights. They are particularly vulnerable to Stomp, but there's no reason they have to be eligible for being stomped at all. It doesn't forge any kind of narrative when the most skilled warriors in the universe (be they bio-engineered or summoned from the Warp) fall NOT to the superior armaments or concerted efforts of the foe, but to being trampled....
I look forward to your thoughtful and measured comments.