First off, a hit assist + a throw attempt makes punishing with neutral jump falling normals not possible.
Secondly, in a lot of cases neutral jump falling normal is not fast enough to punish a throw.
Yo let me try out rising normals real quick
For example, unless Peacock has jumped before 2f into Filia's throw animation, she can't punish with nj anything.
And if Peacock IADs instead, she will not be able to block if Filia also called an assist. So L Bang is a better choice in that situation, since both lose to lows but L Bang beats throw + assist.
Just tested, Peacock can punish with instant nj.LK adf j.MP on meaty Filia throw, which prejumpframesidkwhattheyare+10 startup frames in j.LK is probably faster or around the same speed as L Bang? Please give numbers on prejump frames. For this situation, if instant j.LK is faster than L Bang, then it it superior to L Bang vs Filia throw+Non Anti-Air assist; If they are the same speed, then instant j.LK is superior based on reward alone; If L Bang is faster by a couple frames than instant, then L Bang would be the superior option.
(Also, Robo fortune can nj.MK link j.LP punish on meaty throw, but M Danger is 10f while j.MK prejumpframes+10f startup so there's that)
You are also conflating two different assist timings - One where the assist timed well enough for throw->next frame strike to occur, and another timing where the opponent's assist is delayed enough for it to not even land and start up because Filia was counter hit out of her throw by L Bang.
In the first timing, it indeed does beat IAD j.MP and nj.LK, but it would also beat L Bang clean as well. 7f throw startup vs 16f L bang startup, with the assumption that throw is meaty anyway and assist is hitting within the next couple frames. This means that the Normal Throw escape options in this setup are throw tech, upback or invul super are required, with upback or invul super only being forced on command grab +assist setup upback results in chicken blocking the assist which limits the setup lockdown assists and anti-air throw assists which are mentioned later.
The second timing is best with air throws since air throws are a forced tech-the-throw situation with characters that don't have invul air super(which peacock and robo lack), since if they get grabbed they get grabbed and if they get thrown they have to block a lockdown assist. Quite nice. However, with ground throw + lockdown assist, this timing is not nearly as good because IAD, rising, or certain big falling normals will punish the ground throw early enough to potentially get a happy birthday, with more reward than what L Bang would give.
EDIT: Now that I'm less tired and I look at it again, the second timing where Filia gets counter hit cos the assist isn't out yet, I mixed up with an actually useful timing. If Filia would get CH out of her throw by L Bang and nj.LK, then the assist would just come in to taunt and leave if the throw got teched since throw tech makes assists stop coming out. Happy birthday if they reversal super too, only useful against upback.
If there were any throw-invul air specials, those would be TREMENDOUSLY more useful than the ground throw invul moves in this game.
However, jumping loses to Excella/A-Train and doesn't get you anything vs assist+throw, whereas L Bang beats both of those things.
Defeating an entire class of setup that the character would otherwise have no way to avoid is not too specific a reason to include a move. Eliza gets run all over by setups like this unless she can Lv3, for example.
Well, if you insist. I think that using Bella/BB's other good assists results in a more consistent team, and that using that kind of setup is less sub-optimal than choosing it on PW who has legitimate choice between multiple mediocre assists, which results throw-invul moves ending up being designed for use against teams with less-consistent assist choices with two characters and one specific character with multiple mediocre assists in team composition.
Since you think those considerations are dangerous enough to include moves in your game to specifically combat them, well, I can't really argue against that, that's what you think is important and that's what you're balancing against.
I think you dismiss too many things for the wrong reasons.
For example, Akuma's F+Strong overhead is throw invincible in arcade 3s due to a bug. Throw invincible moves in SG have fewer downsides and more upsides than that does!
Because throw is such a common and repeatable-when-not-dealt-with mixup option and conditioning tool(I'm gonna throw you 5x in a row until you learn to deal with it whoops here comes the throw whiff punish/counterhit), I'd argue that Akuma's throw invul f.MP is not actually gimmicky in 3S, especially if you do guard-for-six-frames-f.MP OS timing. somce his f.MP is throw invul and in this timing it to beats meaty/throw mixup while inducing damage for attempting the throw mixup, and also hitting them overhead if they commit to block low vs DP. It's not a bad option when it fits in with the considerations of the rest of his moveset.
The context in which both moves exist - Akuma f.MP in 3s, Rofort M Danger in sg - is absolutely important when it comes to their valuation. An offense without throws in SG still consists of high/low/left-right mixups pushblock baits and frametraps, which is consistent enough to open people up a lot of the time, but having an offense without the threat of throws in 3s is not nearly close to as consistent.
I also think you and Dime are just plain wrong OFTEN and that this mostly stems from a lack of good competition to prove otherwise / help you learn differently, or lack of having played many games at a decent level so you discount any kind of human factors.
I'm working on it - I'm exploring playing JP players in SG, core SG players in AU have made some important improvements recently, and I'm playing other games with numerous better players more consistently (primarily Melee and Melty Blood right now since Melee is hueg in melb locally and MB has a dedicated online playerbase of actually good players in AU). I've made extreme improvements recently with no signs of halting the improvement momentum, so I'm excited about that.
Also, being potentially wrong a lot an important step to being much-more-correct in the future, so I'd rather you not discourage discussion by implying being wrong is bad. It's only bad to be wrong when you're insistently wrong without addressing evidence to the contrary.