Profile of MilkaCow

Yes, Katyusha is overperforming at the moment. It needed a buff, but that was vastly over the top. There are some reasons why it can't be kept that way:
- Overall damage output: 16 rockets at 160 damage are 2560 damage. That's sufficient to instakill all Oberkommando trucks. A single Katyusha, a single barrage. It needs 13 rockets to hit.
- Flight time: The Katyushas rockets fly for a far shorter time than the Walking Stukas. Stuka gives you a chance to react and spread your squads, Katyusha barely does, especially if fired from anything but max range. You should be able to predict where the rockets impact AND be able to react according.
- AoE profile and damage: While the Walking Stuka has by far the best AoE profile, the Katyusha is now a close second. Taking the squadsizes (and formation) into consideration they should have the same chance to instawipe a squad.

None of these are things that can easily be balanced out by just increasing the cooldown. If you remember the old Walking Stuka - even 5 minute cooldown would've still kept that unit useful. They actually need to be changed, but in a way that still keeps the unit useful. 100 damage on the rockets would still mean it could oneshot the FlaK HT if all rockets hit, so I fear it really needs to go back to 80. This can be compensated by a better AoE profile and maybe more penetration (or giving it crew stuns or whatever). The alternative would be probably something that shoots less rockets, but still at a high damage. Right know it deals twice the damage of a Walking Stuka and in a smaller area, making it far too good against static objects.

Well, now you guys know how the commanders start out before balancing

Yes.
3.0 normal repair speed
+1.0 with vet2 I think
+1.0 with Support Package

Of course penal flamethrowers can explode. All flamethrowers have that chance to explode.
I personally think the upgrade is great. Besides building clearing it's awesome against the OKW elite infantry. All those "incoming accuracy modifiers" or armor or such that make their infantry harder to kill, especially with vet - Flamethrowers ignore that. A flamethrower doesn't differ between a vet5 Obersoldat or a cheap Rear Echelon.

I think there are a few questions to answer first:
Vet 3 = 1.6 unit value
Vet 5 = 2.0 unit value

So Vet5 is far more potent. The requirements for Vet3 on the Oberkommando and Vet3 on other factions are the same, Vet4 and 5 are just additional vet levels.
Vet1 = 2 * unit value
Vet2 = 4 * unit value
Vet3 = 8 * unit value
Vet4 = 10 * unit value
Vet5 = 13.3 * unit value

Those two unit levels for OKW are their flavor (like US gets crews), so I don't think adding it for all factions is good. Yet I don't think 5 levels with units performing twice as good at vet5 is good. I'd rather have Vet4 and 5 easier to obtain, but give a smaller bonus.