Very true - I forgot that the megaboss's command ability was at the start of combat (As well as the warchanter's prayer). So, yes, the deepstrike option is best as part of the usual whole-army assault with the megaboss + the waaagh.
I don't think the difference is as substantial as many think. Assuming a full unit of 3 make it in to fight, Pig-Irons do 5.8 in all fights while Gore-Hacka's do 6.9 on the charge and 4.5 if they didn't charge, all at rend -1. So, over 2 turns of a combat (assuming the combat stays the same), they are pretty much even. They scale equally with +1 damage from warchanters, so they are even there.
I think gore-hackas may have a small tactical advantage in a real game, as you'd probably prefer to front-load damage on the charge if possible and the 2 inch range helps with bulky GG bases. But, that being said, I think the two are actually more equal than people have stated. They are at least close enough that no one should feel screwed-over that they modeled all of theirs with pig-irons up to now.