I understand that this thread has more or less degraded into a stuka vs katyusha debate, and though I don't think it should be the focus, I realize why that's what the topic is. So with that disclaimer in place.
If we look at these two units separately, which I believe is necessary as they are two different factions functioning against two different enemies, I think we can get to real discussion.
The reason so many people are baffled by the katyusha's effectiveness is honestly, how devastating it can be to the German armies, but more specifically OKW. I'll focus on OKW and RU as that seems appropriate lately. With economic strains, veterency emphasis, and elite unit preservation in mind, the katyusha is simply far too punishing. I haven't played a game since the update where either myself, an opponent, or an ally has not preemtively retreated at the sound of katyusha fire and STILL lost a full squad (often vetted) outright within the first wave. There's still three more. This also isn't considering the issue that OKW is built on a foundation of building decisions. Currently, the katyusha makes that decision for you. In two waves of barrages, whatever truck you deployed is gone.
Now, a lot of people have argued that "well, that's your fault for being aggressive, pay the price." That MIGHT be valid if that was the only realistic way of uprooting these bases. But we all know it's not. Furthermore, this is not just a unit that destroys bases, it goes from blob control on an extreme level to killing off a single squad attempting to capture a point.
The stuka is a separate topic.
The stuka is useful for blob control, and while yes, there is a strong chance a few units may be wiped depending on the group's size, unless the units are marching in a very careful and narrow line on a very predictable path, you're not going to have the same effect as if a katyusha was firing on that same collective. THAT right there, is not a problem -- the problem is how horribly strong it is currently. Let me repeat that. I do think that if you had two of the exact same groups moving in the exact same manner and hit directly by both a katyusha and a stuka, the katyusha should be awarded the higher death toll. I don't like homogenization. I like when differentiating units have differentiating strengths and weaknesses.
The stuka, I feel, shines in very certain scenarios. Clearing out buildings and hitting a set up line. However, when a line, perfectly centered, is squared up perfectly and fired on, you rarely squad wipe healthy and repaired set up squads. Infact, I'd say a third of the time the artillery skips a beat and all but takes a few models. That's not a problem either.
Just to get this out prior to counter points because I can feel this one creeping up fast; to compare mobile blobs and the effectiveness of each is almost silly. The targeting reticles themselves should be enough evidence of that. It's like comparing the effected area of a streamlined laser and a shotgun.
All that said. This shouldn't be a debate where the validity of the subject is justified by another unit.
i think you're forgeting a few important things regarding stuka. There are chokepoints or obvious retreat points in many maps, like, say, the roads on semoisky and kholodny.
So is isn't hard to predict these and wipe them, especially if you fire it behind a unit taking damage in a fight.
Outside of a fight, sure you can move to the side to avoid it, but when you're fighting sturmpios, or any strong okw unit you can't afford to delay your retreat.
Also losing squads for SU isn't just a minor inconvenience. If you lose your vetted conscripts or penals or guards, what are you gonna do with vanilla scripts against vetted okw or even obers ?