In EF, the Calliope fires a 30 missile salvo, the Kat 16, the Nebel 6.
The 25pdr also fires a barrage of 6 shells, it just seems more because they're "spread out" unlike the Neb (also because they're much more powerful).
If the Land Mattress were to be in game, and if it would replace the Priest, it'd be fairly different, for starters, it'd probably only do a missile salvo of between 10 and 15, it would not have access to supercharge (these were shells, not rockets) and victor target (because of limited range), mix it with a slow movement speed and this would probably increase the chance of the opposing players being able to steal it for their own purposes.
The land mattress would probably have its damage between the Cal and the Neb, and have a nice long(er) cooldown because of all the abilities it could use (afaic, the Walking Stuka rockets have the highest base damage of unit-based artillery (120-100), Nebel has the lowest (30-20), this is not counting any possible modifiers).
Very alternatively, maybe we could replace the FOO from a 25pdr off-map barrage to a rocket barrage, only Axis have these.
