Profile of MMX

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I am not saying the ability is great but that comparing scatter areas would mostly make sense if all rocket landed simultaneously or if one was aiming at static target.

the thing is that the scatter of even the first salvo of 4 rockets is way larger for the creeping barrage than for the normal one, which costs you munitions on top of being worse. i'm just not seeing any usefulness in the ability at all in its current state

The scatter of the creeping barrage is so large that I'd go so far as to say it's completely useless. This has something to do how scatter is calculated in this case, and might also involve a potential bug in the implementation. Allow me me elaborate:

Most of you will know how scatter works in CoH2, and if not, there is a comprehensive guide to look up the details here.

So in short, there is 'box' around the targeted point for every unit that defines where shots can land in. The far end is usually a bit wider than the near end, but the exact size and shape are defined by the distance and other, unit-specific parameters. For the normal Katy barrage, it looks something like the box on the right in the picture below.



However, in case of the creeping barrage there is an additional box as shown in the middle panel (approx. as wide and long as the in-game indicator). The box is divided into sections, which become active after a given number of shots fired or time elapsed - this is basically the creep in the creeping barrage.

Now each random point in the box, or active section, is NOT where a rocket will impact (the red cross), but rather defines the center point of the scatter cone of each rocket (the blue cross). That means scatter for the creeping barrage - even the first salvo, is much greater than for the normal barrage at any distance (left panel).

And here's where the presumed implementation bug comes into play.
The Katy, as many other units, has several hardpoints with different weapon profiles used for specific abilities. This way, mortars for example can have lower scatter and lower reload for their barrage ability than for autofire. In case of the Katy, there is a rocket profile with high scatter used in the normal barrage ability (hardpoint 2) and a low-scatter one (hardpoint 3), that gets called by the creeping barrage and the (long gone) precision barrage.
However, there seem to be two separate creeping barrage abilities for the Katy in the editor (katyusha_rocket_truck_creeping_barrage_mp and katyusha_creeping_barrage_mp) - and as you might guess at this point one calls the low-scatter hardpoint 3 and the other the regular, high-scatter weapon in hardpoint 2.

So, since the current creeping barrage ability for the Katyusha uses the same weapon profile as the regular barrage, scatter is atrocious and the ability practically worthless. I'm not sure if this got changed by accident back when the precision barrage was purged from the game or if there's any other good reason... but in my opinion the creeping barrage should be reverted to use hardpoint 3 instead. That way it would still have quite significant scatter, but at least it wouldn't suck way more than the regular barrage at any given scenario except burning munitions.

wow, never really run the numbers before but you're right. in most cases the deviation should be indeed miniscule at best.
a quick calculation ( acos(0.95)*2) shows that the scatter angle would have to exceed ~36° to have more than 5% difference - which out of the top of my head not even a howie firing into the FoW would achieve.
if it saves time and effort, your approximation is probably totally adequate

Strategy forum would imply there is something wrong with player using it, not the unit and we all know every single CoH2 player is a seasoned high end tournament player who never makes a single mistake, so natural conclusion, obviously, is a balance problem, always.

spot-on and accurate!

but to the op's question: if you want to see how to use the m3 creatively and (sometimes not so) effectively i recommed watching vonivan's stream

I'm currently working on a proper implementation for off-map arty to the spreadsheet and was wondering how exactly the scatter randomization is calculated in-game. So far i found the radius of the (circular) scatter area in the abilities tab and I assume the center of impact is likely derived by randomizing the distance (between 0 and the given radius) and angle (between 0 and 360°). However, that would mean that the impact density per area would not be equal throughout the scatter circle and more shots/m^2 land close to the center than near the outer edge of the circle (i.e. probability is proportional to r).
On the other hand, the center of impact could also be calculated by picking a random (x,y) coordinate inside the circle, which would result in an equal shot density everywhere in the scatter area (i.e. probability is proportional to r^2).
Does anyone know the specifics or has anyone ever tested this?

Additionally, the offmap abilities seem to call a standard weapon profile to determine the damage and AoE properties, which makes sense to me. However, I'm not sure if and how the scatter info of the weapon (angle_scatter, distance_scatter_max, etc) is taken into account in the scatter calculation. Does anyone have info on how this works by chance?