You can make fun of my comment if you wish, but the Kat is supposed to provide you with a help to defeat the elephant. If you are T4 you need a long range unit to wear down the elephant, the kat can fill that role.
Yes penetration is worse, but they can prevent elephant from being repaired and force it to move. They also let you know where it is in the FOW.
tried it, didnt work.
katyushas is abysmal against elefants and misses so much in the fog its hard for them to kill even supporting units.
giving sight of the elefants is barely any use when the commander has recon planes to spot and halftracks still cant reliably kill recon planes.
while it is 'supposed' to be of some help, it is not the same as 'effective'.