Panzerwerfer and Ostwind should swap places and this is why:
(1) The Ostwind requires just as much fuel as the P4 for less utility. By the time you field an Ostwind it will meet T34's or an SU-85, the first is a problem but the last totally prevents you from using the Ostwind in any meaningful way. Same fuel, more risk, for less utility than a P4. By every calculation a P4 makes more sense.
(2) German indirect fire options are meager and it got markedly worse after the Panzerwerfer was moved from T3. That's when we starting seeing the MG and sniper spam tactics rule. They still do to some degree. MG spam is still a huge thorn especially in maps with houses. Snipers still almost have no counter. Especially if there's one Su-85 on the field preventing an ostwind or P4 from getting to them. German mortar, despite the changes, aren't doing anti-sniper duty. Panzerwerfer is the balance here, for both. Again, these tactics were always in check before the Panzerwerfer move to T4.
(3) Swapping these units causes no imbalance for the soviet player considering they have the OPTION to build T4 anytime they want, they have no HQ upgrade's to go through. It's a tactical decision for them. So moving our T4 unit to T3 is not a balance issue on the Soviet side. And besides, they build direct T4 now anyway every time and have since early beta.
(4) This needs repeating: The P4 and Ostwind are redundant in the same building. T3 comes at a time when T34 or Su-85 are already on the field, forcing the decision to a P4 every time.
The more I think about this the more I feel it's strongly needed.
I disagree with idea of swapping the two.
To respond to your points in kind;
1) I'm not sure I really agree with this assessment. The Ostwind is far more effective against infantry and thus it makes itself vulnerable to armor counter attack for a shorter period of time. It kills infantry faster and forces their retreat thus an SU-85/T-34 has to react faster to it's positioning. Keep in mind that the Ostwind can fight toe to toe with an T-34 in the current balance. The SU-85 is a danger to the Ostwind but it's an equal threat to the P4. You can't pit either tank against the SU-85 without losing most of the time. The Ostwind can accomplish its job though and when supported by anti-tank infantry can force away Shocks and other dangerous infantry in time to save Pak40s and PGs who can in turn pressure the SU-85 away.
2) German artillery is unit for unit far better than the Soviet ones with the exception on the 120mm Mortar which doesn't really have a parallel and is doctrine locked. The Panzerwerfer's cooldown was accelerated in a recent patch to match its T4 place. It's better than a Katyusha. The Leif Howitzier is way better than the Soviet counterpart as it can fire 90% of the time and has greater accuracy. The mortar re-balancing probably has the German mortar ahead of the standard soviet 82mm.
Comparing unit to unit is largely pointless though, I admit. The context of units matters more than their raw power more often than not. Still, I disagree that Germans have the weaker indirect fire.
To be honest I don't really understand your (3) point. I'm not sure what you're trying to say. Any balance change is going to affect the Soviets. Having to worry about cheap and quicker Rocket Artillery is most certainly going to change the balance of the game an Soviets will have to respond. I mean you admitted that it
could have a profound balance effect. When rocket artillery hits earlier and can punish AT guns and Maxims that's going to make Soviets reconsider buying those units.
I like the Panzerwerfer in Tier 4. It was very strong in Tier 3 and I felt like this was a good way of balancing the game while also making T4 have something to offer other than "heavy tank that costs 150+ fuel".
Honestly, I agree Tier 3 is really boring and bland. It gives you a medium tank, a specialized medium tank or a medium assault gun. Your solution sort of just shifts the problem though. Tier 4 already has a dedicated anti-infantry tank: The Brummbar. It sucks. No one builds it. I'm sure everyone would ignore the Brummbar for the Ostwind if you actually swapped them. That's assuming they bother with Tier 4 at all because the only useful thing remaining will be the Panther. Is that better?
I think the better choice is to balance underutilized units until they gain some relevance in their battlefield role. I actually think that the Ostwind does have some of that relevance right now. It's a good unit for the price. Pushing it back by ~90 fuel in tiers
will cause it to become useless. Whereas the Panzerwerfer is useful and valuable in it's current location.
I think we would have seen the rise of Maxims and Snipers regardless of the swap. They weren't used because the game was still being explored and a strategy like "build 4 MGs and use them to capture the map" is so outlandish that no one would gravitate to that strategy naturally. So its discovery was slow and other balance changes were happening independent to its discovery.
edit: Wow that a long post.