Oneshot is vehemently pro-2d20.
So, let's start off with this point. I'm in no way "vehemently pro-2d20." There are quite a few posts I made on this board, and many others on the Modiphius boards, where I point out things I don't like in the system or things other don't or wouldn't like. In fact, my first post in this very thread notes I think there are too many niche/fiddly options for some of the subsystems that make those systems too complicated. I'm hardly a sycophant for the game.
Also, the math thing is a complete red herring. You're avoiding the actual points I raised to harp on a few words for a minor point in the post, while ignoring the actual argument I made. I don't know how to code; I'm old and like formulae. I used a formula from my college stats book (that actually used two dice rolls as the example). Maybe I did bad arithmetic, but I can't tell from that code you posted.
But that's OK, let's use your number. A complication still only occurs 9.5% of the time on a normal task. So it's still less often than rolling a crit or a fumble in D&D, right? So still not that often, relatively speaking? I guess that depends on your personal definition of "often."
I'm actually glad you did this long post, however, because it highlights what I think the real issue here is and what explains our vastly different play experiences involving complications and threat:
I've had sessions where the rolls were bad. Very bad. The complications opening the threat range being story appropriate, resulting in 2-3 more complications generated per roll. I had a session, with 2p, end with 20 threat, the players both with threat ranges of 16-20, and 3 complications each as trait penalties... there was, at that point, not much more to do to them other than kill them outright. I've had multiple sessions end with 10+ threat, and a mission failure, and no shortage of complications imposed.
So here's perhaps the first disconnect. Players don't have "threat ranges," tasks do. "Some circumstances can make a Task uncertain, though not necessarily any more difficult. These factors increase the Complication Range of a Task, making it more likely that Complications will occur." P. 83. "You can also increase the Complication range of a Task, given the circumstances of the scene or the Task." P. 279, from the GM chapter. Emphasis of course mine.
If you're slapping complications on players that have them walk around with permanent increased chances to roll complications, of course they're snowballing into more complications! But that's not playing by the rules as written, at least as how I read them. Increasing the complication range, by my reading of the rules, is a fairly rare thing, but it appears you do it all the time.
Complications, per the rules, "may impede later activities, or they may simply be inconvenient, painful, or even embarrassing." P. 82 of the core rulebook. Complications don't automatically have to make life unbearably difficult for the players. Complications can also affect the other side, not just the PCs, and so can be an aggregate neutral. And they can be removed by a simple Task (p.78) or a spend of two momentum during a related task (p.85). Do your players never remove complications when they occur? Mine do all the time. Or do you make them so difficult to remove they just fail at it?
I use complications to create interesting wrinkles in the game or to cut off options without making it impossible for my players to still have success. The complications usually last only for the one scene or one task and are not permanent markers on the players that affect all of their tasks for the rest of the session going forward. It seems like you did the opposite at your table, and not based on anything written in the rules but on your own GMing style. So if it was a problem for your group and created a resulting play style that was more difficult and deadly than your players prefer, that's not a fault of the game design.
Most rolls I've seen are NOT on 2d20; typical is about 3. Yes, even if it means spending threat, my experience is players are going to roll at least as many d20's as the difficulty most of the time. Also, the adjustment for increasing threat range for extra help is retained... which prevents "Dogpile on the task" but also puts hard tasks more likely to generate massive piles of threat.
From an "Angry DM" mode, it's a great way to discourage players quickly.
How high do you set your difficulties? Base difficulty in the game is 1 or 2. P. 278. My PCs would roll 2d20 on the majority of rolls, because the majority of task difficulties they faced were 1 or 2. They definitely pumped them up when they needed to generate momentum for their pool or had a task with a higher difficulty, but that was a minority of the time. Which would actually jive with what you state about rolling at least as many dice as the difficulty. So if your players' typical pool is three, does that mean your typical difficulty is 3? Because that's significantly higher than the advice/guidance the game gives GMs.
It's obvious to me that those who don't see it as an issue are not terribly perceptive - because the way the adding hazards works, it only takes 5 threat to kill off a PC in fairly short order... if you have more than that left, you have OBVIOUSLY not used the threat to it's maximum, and have thus given any success straight over the table... and for the perceptive and mathematically competent, that's clearly "I didn't actually accomplish it." It makes it ring hollow.
Might be accurate to the show that way, but it's not good gaming.
Or, alternatively, you ran the game on the highest difficulty setting, and your group didn't like it. The fact that you feel there is some need to spend threat to its "maximum" effect tells me that you take an adversarial approach to GMing. Which is totally cool, if that's what you and your group like. But it's not the default the game assumes.
At my table, complications were relatively rare, probably because I set lower difficulties than you did and didn't increase the complication range on tasks very often. When they occurred, they made the game fun and interesting by providing unpredicted setbacks. Those setbacks never hamstrung the players or otherwise prevented them from succeeding in the mission, because I didn't design them to do that. Maybe that means I'm not engaging in "good gaming" in your opinion, but my players and I had a ton of fun. So I will take your bad gaming any day of the week.