Onslaught is definitely an "elite" level STF. It puts Cure Space Elite to shame. It's also obvious that this one is not a DPS-run, like the rest. Onslaught requires strategy, which is the whole point of STFing. The team that I went into Onslaught with for the first time did awful because we had no idea what to expect and Onslaught was completely different from the existing STFs.
I look forward to seeing how a prepared team handles it
Personally if they were to touch the existing STF's would rather they make it more on par with actual game rules. No cheating borg, no invisible torp one shots, no walking through walls, no invincible cloak (i get it's scimitars "perfect cloak" but even then the shields would take damage), no none heavy tac mowing down a single group with a spread, or having a single super tac cube on steroids just because it was easier than making two regular tac cubes or a strategy(KSE vs ISE).
As for the New ones, i like that they're tactical in terms of planning and teamwork equals success, not DPS=awesome, but at the same time, the damage outputs are too high. With teams in full MK XII stf gear, a single normal tac drone should not being almost wiping out the shields and health of the whole team in a single spray. The Queen and elite drones i can see doing that, the heavy tacs, maybe here and there, but the smaller drones not so much.
Adding in the cage rather than just the lock out was a great idea as well. Being taken out of a game sucks, but when it's possible (not easy, just possible) it makes that time so much better. The floor panels and platform were a nice touch, although i'd rather have a plasma or electrified floor since falling that far usually doesn't do much damage, something there to indicate insta-death aside from a shortfall would be nice.
The rewards given in Hive Onslaught Elite are not worth the time and pain of that mission. The mission is interesting, but it takes forever to grind through and you are going to explode 10 times before you are done, even if you are playing smart. Raise the rewards on that one by at least tripple and I'll play it again, otherwise I will stick to the other STFs.
I agree with the OP that the other STFs should be brought up to Onslaught's level of difficulty.
Let's face it, the NPCs in Onslaught are far more realistic:
Seemingly more intelligent
A better level of damage output (I never got 1 shotted)
It was quite refreshing to actually have to THINK (I know, it's shocking) about what was going on and prioritise targets as necessary. Onslaught is difficult BECAUSE it's not a DPS race with in my opinion is a good thing.
A lot of peeps will prob start complaining that they're not guaranteed to get rewards any more, so maybe you could have it like some of the FAs where rewards are doled out progressively as you scale through the mission.