Brand said:
True, but I don't think I've yet seen (or run) an encounter that called for a single Genestealer to attack an entire KT. The Dev may want his Assault buddy to help him out, but if the Assault Marine is dealing with one or two of his own opponents he won't be much immediate help. Other things can cause issues. For example, the section of Final Sanction where the KT travels through the pipes and the valves seal off one member to be jumped by Genestealers. The SM may have to fight solo for up to 3 rounds before help can get to him. If the Dev gets caught in that situation and can't move, he has little chance of survival.
And as for the "full withdrawal" vs. "just moving" - that's exactly how the book handles it. Just moving back to shoot, you can't use a Reaction since it's your turn. That's the price you have to pay for (hopefully) gunning down your enemy. Being defensive and disengaging means you protect yourself, at least for a short time. I've mostly seen that it's best used for a SM to move out of the way so that another KT member can gun down the attacker without the penalty for shooting into combat. Melee fighters like the Assault Marine usually prefer to keep everybody in melee so that they can take advantage of Talents like Double Team.
In the case of the whole party getting jumped, there's a lot to be said for those who are... I won't say inept, because we're talking WS of over 40 and +10 damage here... but less awesome at melee simply using the all out defence option in order to survive until the AMs have killed theirs and are available to help. That's the sensible option that uses good teamwork. If the Dev is too impatient to do so and is more interested in individual action that teamwork, then there's a price to be paid, just as AMs who rush off with a jetpack to go and kill stuff before the Dev has softened stuff up deserves a spanking! Likewise, if the Dev lacks the patience to wait and wants to step out and shoot, then I also think that there's a price to pay. Marines have the Patterns to represents their teamwork, and there's more to that than simply a mechanic for doing funky stuff with Cohesion: There's actual teamwork! I'm a massive fan of encouraging teamwork and good tactics, because one of the game themes is supposedly about building that teamwork. If players are always thinking of number 1 and it never hurts them, there is less incentive to work together.
In final sanction...really... if the Dev is pointman or tail-end Charlie then that's a bit of frankly poor tactics, and my mercy would be paper-thin! In close quarters with confirmed genestealers, any party with a bit of common sense has melee characters front and back, ready for just that kind of thing.
Stupid and selfish assault marines might like to keep everyone in melee so that they can get their +20, but decent ones would almost certainly want the Dev and other shooty types to be kept 'clean' so he can keep firing.
Coming into this discussion it seemed perfectly reasonable to allow the reaction to be used to parry a free hack. But the more it's discussed, the more I'm coming down on the side of 'no'. I'm also not keen on shooty characters basically abusing the ugo-igo initiative to run and gun their way out of melee, but aside from inventing other mechanics to deal with it, I'll probably just limit it purely by disallowing reactions against free hacks.
[although given their razor sharp quality, it's kinda moot. You might as well be in your pants. **** genestealers]