this are the sec u have to react--- testet with a stopwatch:
STUKA: 5,97
PW: 5,89
KAT: 3,08
CAL: 4,19
LM: 2,82
All that time and effort wasted. If you want to continue doing test then:
-How long does it take to unload all the payload for each barrage (from the first rocket till the last)
-For the 4 rocket artillery (Stuka zu fuss can't be really consider a rocket artillery in the same sense as the other 4 since it unloads a barrage with a fix position and increased damage), how long does it take to land the first 8-10 ROCKETS. (The single rocket barrage from the PW, the 2 barrages from Katyusha, the first barrage from CalliOP, the 10st rockets from LM).
If you spend less time in the forums and more improving in the game you'll realise that what you are trying to prove is pointless as each of the 5 pieces work quite differently.
TL;DR: you are making blind tests without realising what's wrong with the unit or which direction it should be nerfed. We already had the same problem with CalliOP were it got proper nerfs (decrew) but didn't solve the 1st/2nd wipe barrage (should kept the 3 barrages with an increase in the gap and give them equal amount of rockets)
As i've been saying on this thread: give it a proper veterancy (remove the vet2 bonus) and see where it stands. If further nerfs are required, increase fuel cost and/or slower down the RoF while keeping the amount of rockets (cause firing lots of them inaccurate is the essence of the unit).