To start, this is a VERY long post. And also, these ideas for balancing would make some things easier, AND some things harder.
So I was reading down in the Tribble area, about how they are altering the insta-death attacks on the Hive Onslaught mission, and Bort even said that pretty much, instant death attacks are frustrating, not challenging.
So I got to thinking about how the other STFs could use a balance pass on a lot of things, for the future. Not right this second with season 7 so close, but maybe a few weeks from now or something.
A lot of this stuff primarily is for the elite level STFs, not as much on the Normals.
I'll start by putting some of my answers from that:
Instant-death isn't good. If you can't counter it somehow, it shouldn't one-shot you. Examples include Donatra's torp spread, her Thalaron attack, Cube Heavy Plasma Torpedoes, and so on.
Donatra's Thalaron attack and all the Heavy Plasma's Cubes can fire can all be countered. The torps can be shot down or use something like TBR on em, and Donatra's attack can be out-right dodged. However, something like Donatra's torp spread, not so easily dodged or countered, almost always kills regardless of anything else.
I'm not saying things shouldn't hurt, just that some things shouldn't just be a guaranteed death sentence with no way to stop it.
Same thing applies for ground as well as space, especially from the bosses and any level of Tactical drone. They fire so hard that you are guaranteed to lose your entire shields within moments, possibly with death if like an Elite tac crits you. Only max or near max points in PS Generators and/or shield resists running will prevent your shields from draining after the first shot...usually.
The Borg need sustained DPS (someone else's idea, not mine, but one I agree with). Pretty simple, keep tanks having to focus on tanking, possibly with a healer to help, but without all these super-hard hitting attacks. I would prefer giving the Borg more weapons, especially cubes, and lowering the damage of each weapon, but letting them attack with more weapons. It'd help further if their plasma beam arrays were all 360 degrees to keep up with sustained damage.
That's some general thoughts, now for more specifics:
Infected space: Not much to say here. Aside from being the most completed STF in the game, and generally the easiest of all space ones, it's honestly ok to me as is for the most part.
The biggest thing I feel would have to be the Tac cube, more than just the DPS thing as mentioned above. It should have an escort, like in normal, several probes would come with it and maybe a couple spheres, and in Elite, it should have all Spheres (no cubes, mostly because of possible clipping issues and such).
Infected ground: Again, most of the normal mission is ok as-is. The optional is very annoying, but doable with a team, even on elite with coordination and team work.
A problem I feel is the invisible trigger lines. There's no way to know where they are without someone telling you exactly where they are and what to do. In normal at least there should be something telling or showing you not to go past a certain point, to allow people to learn it.
Becky's room is where the bigger issues lie. On normal it isn't as much of a problem, with the paths letting you walk right where you need to go. On elite, falling into the goo is a death-sentence, but it shouldn't be near-instant, and also you should have immunity to it for at least a short time if you are revived, along with having more areas to jump up easily without HAVING to be a Caitain or Ferasan to get back up.
Becky herself is tough because not only do her tactical drone friends respawn at a rather quick rate, and that she chain lightning's you over and over, again, without much way to counter it (see above on things that kill without being counterable).
Cure space: So the hardest of the three current space ones, really only needs again, a tone-down on the insta-death, mostly the Borg Negh'var Iso Charges. The Carrier could use a boost though, it normally just sits there and dies really really easily. Give it some sci abilities, might make it better, like Gravity Well and such.
Also, an escort as well could help, a couple more Negh'vars and Raptors would help at least make it take more than 30 seconds.
Cure Ground: The mission again feels pretty good as is, but one thing has always bugged me: Cover Shields are pointless. I know they can prevent Worker Drones from getting to the transformers, and having the auto-kill on em keeps that from happening, but it also completely negates any usage of a captain ability on the ground, a thing the other two classes do not have. There are a lot of wide spaces, with little to no cover at all, and the cover shield can give that. If you don't want it to be used as an exploit, ok, but don't completely prevent ANY use of it though.
Armek: He's alone, so that's ok. The biggest problem is all his 'cheese' he has, mostly in the form of the neverending orbital strikes. Again, one-shotting attacks aren't good, and these are not easy to see (not to mention possible lag and the issue of it blocking your view of the fight). His ballarina twirl is fine, but maybe it should be more a big push-back attack, than such a raw, shield-penetrating melee, it can be wicked if it crits.
KA Space: Again, a tac cube is alone. It needs more to fight at the start, make it a good beginning battle. Perhaps probes or spheres in normal, but potentially cubes in elite (there's a lot of open space, so they could fit). Donatra, again, less insta-death without counters, mostly her torp spread. Aside from that, she needs to have cooldowns on her abilities, including her cloak. She seems to use a lot of her abilities over and over all at once without pause or a real AI to em.
This again would be a good excuse to add an escort to her, show off some Borgified Romulan ships.
KA Ground: Moving the optional timer back to the first room puts the mission more on line with other ground STFs, so that's ok. The mission is the easiest of all three, but adding more tough enemies wouldn't really help.
Tosk though...is a joke, his drone buddies are the only real issue here, and they can be lured out into the hallway or bottlenecked in the doorway then exploded to death in many various forms. Sure he can use psionic attacks, and they are annoying, but aside from that, he has little going for him. Unlike the other two bosses, his room is also very small, and much more of a 'side room' than a 'final boss' area really. He really needs some improvements to make him tougher.
the counter that I use for her torp spread are the combo of brace for impact and tac team. it heavily mitigates the incoming damage, even in an escort. another thing that I use is the SNB captain skill for my sci toon. I make sure to engage her from behind, let her charge her three skills which you can see pop green on her avatar and then snb her, leaving her vulnerable and declawed.
as for the iso charge from the negh vars in CSE, they should always be focus fired upon by the team when it spawns. also, have the person behind it, usually the one that will hold aggro attack it first, so it has to turn 180 degrees to use the iso charge skill. this buys everyone time. then pop the sucker and no one has to die unnecessarily.
as for donatra and her cloak, the easiest way to find her is to lay a couple of aceton assimilators close to her and to follow the blue energy trail. pet spam works well too, as with danube shuttles and whatnot. they will follow her even while she's cloaked. boost your aux power to max and head to her general area and her cloak will go down sooner than if you were to wait around for her to do it herself.
There is pretty much nothing in current Space STFs that will one-shot you without a counter, outside of an under geared ship.
Donatras torp spread is just brace for impact, and maybe a tac team. You can see the torps incoming, so you have plenty of time.
The Neg'vars are really just a matter of being aware when they spawn, and preferably the direction they spawn facing (be behind them) That's when they like hitting you with an isometric. Even then, an isometric wont one-shot you unless you have absolutely no buffs up (and you should always have something up, either a TAc Team, EPtS, etc) and have already been taking shield/hull damage, or if your bunched up with teammates and catch the tail end of the chain. Both are preventable.