You've made two key changes:
- Allowing multiple combat half-actions per round
- allowing movement to be replaced by a non-movement half-action
The primary factors I see are:
- increase in Psyker offensive capability (Most of their offense is more powerful than their allowed weapons; it gets worse under RT or DW, due to a different psychic system)
- decreased access to defenses¹
- decreased emphasis on movement²
- increased emphasis on non-action defense (IE, cover)³
- breaks the equipment bonuses
- decreases incentives to use burst and full-auto autofire modes
- cybernetics and talents with extra half-actions become devalued⁴
- initiative becomes more important⁵
- Ganging up becomes less essential⁶
¹: Since one gets very few defenses per turn, this change of yours makes them less valuable, by allowing them to be overwhelmed faster.
²: The current system makes movement a valuable and essentially irreplaceable part of the round; take it or not, it's lost if unused or unusable. It's not terribly realistic, but is very cinematic. And DH, RT, and DW are all intended to be very cinematic in tone.
³: At present, especially for melee, active defenses (dodge and parry) are quite valuable; cover is less so, but not enough to render it useless. When one allows replaceing movement with a second attack, cover suddenly becomes MUCH more attractive, as it's an assured penalty to be hit, instead of a roll by the defender... but it also reduces drama.
⁴: At present, the only way to get a second attack is expensive talents and/or cyberware with inexpensive talents. If a character can just hole up in cover and double shoot, these talents are far less valuable, making the Assassin and Guardsman's additional combat actions less useful.
⁵: Further, by allowing the etra attacks, you can run a target out of actions sooner, as well, so initiative becomes more important to prevent having actions drained in defenses.
⁶: Ganging up is the great equalizer in RT and DH combats; it's how one overwhelms defenses. Given that every character can defend once for free, and once by aborting, if you can attack twice, you've just eaten both defenses this round, meaning you only need one attack from a buddy to get through. The norm is that you need two buddies to negate the defenses, or one buddy with a multiple attack talent.
It sounds like you made these changes with rank 1-2 characters... it's going to be more profoundly off-norm or higher rank characters, as normal slow growth of actions is made to feel even slower by providing far less of a bonus over not having them.
I am having the same problem, although my characters just reached level 3.
However, I think that the best answer is for the party to better share the loot between each others. They, after all, are the ones who want to survive, not you.
If you have one player who always takes it all, he will create the imbalance, not you as the DM.
For what to "distribute", I use the tables on DMG p. 136-139. That gives me a way to determine the various types of objects I can give my players. The main problem is to avoid giving them way too powerful items.
However, I do not like to roll on the tables because I prefer to be in control to give the players exactly what they are likely to need (plus a little more).
Also, there are certain things that make sense. If you kill a mummy, it makes sense to find a Staff of the Python and if you kill a Wizard to find a Robe of Stars, for example. Plus, I prefer to offer items that make sense in the adventure rather than random things.
That being said, there is one rule that will limit a player from using all the items. If you look closely, there is a rule about attunement (DMG p. 136) which prevents a user from having more than 3 items that require attunement. So if you offer many of those, the one player who wants it all... would not be able to use the extras and may then start thinking he should share a bit more (because such items in his backpack won't do much good to the group as a whole.)
Another way to limit is to give similar items or items that the user(s) do not have proficiency in (i.e. give 3 short swords + 1, it is likely that people will stick to their existing weapon because they don't have proficiency in short swords. That being said, they'll need magical swords for killing those werewolves...) Also you cannot use two magical items of the same type simultaneously (DMG p. 141). So that's another way. Obviously, that could become quite a bit monotonous... but it could be a temporary solution to get everyone to have a similar power level. And the characters can sell or exchange the extras too.
Finally, there are items that require a specific class or set of classes (see Staff of the Adder, DMG p. 203). You could also impose limits such as race or size or even level... since you do not have to specifically use what the DMG presents. I myself use it as a large set of examples rather than the actual source of magic items in my worlds.
Best Answer
I had a group of 4 PCs taken down by two NPCs wielding Power Axes, light armour. One PC named Garret had Power Armor and full health with a man-portable lascannon. I think his BS was 70 and he was famous for taking down several tanks and even War-Walkers.
Another time I had a first time player have a demon intrude on his ship the first time he ever entered the warp. I decided to simply not tell him, having the demon hide amoungst the crew. However he wanted to expiriment with his navigator power, 'Gaze into the abyss', and happened to reveal the demon. I decided the teach him a lesson about this game, by having him die, spawning Warp Predator (Ebon Geist) whom has killed many good players (and has no weapon).
My plans were ruined when he passed the fear test and, with a pistol, scored 3 Righteous Furries and did something like 100 damage.
Just let the players play, I say. The dice will make the decision in the end. It's better when players blame the dice anyway.