[Marcello]

The warhead size issue would be worth looking into.
Currently I am running a series of comparative tests.

USA vs USA
Two companies of M1A2 SEP placed on the map with identical deployment. The first is bombarded by a MRLS battery. The second by 155mm battery using cluster rounds. The ammo allotments of both batteries have been modified in the editor so that the same number of rounds (24) are fired by each battery.
I am finding out that the 155mm battery is invariably more lethal against the tanks than the rockets.
In real life however a single MRLS rocket carries 644 DPCM bomblets vs the 88 carried by a 155mm cargo round.

I suspect warhead size is at play here.