S3 small template is better than S2 large template. A small template direct hit is going to hit 21 of your infantry in your regiment, barely less than a large template hitting that same regiment, and it's going to deal 50% more wounds.
However, the mortar costs MORE than the rock lobber.
Shooting at hordes? why aren't you taking the new helstorm?
Did you miss my post of numbers? I know mathshammer isn't everyones strong or favoured point, but if people are going to argue about the effectiveness of units then it needs to be taken into consideration. It is not going to deal "50%" more wounds. Even if they hit the same number of models, against T3 units the Rock Lobber wounds on 4+ (50% of models) and the Mortar 5+ (33%). 33 x 2 = 66% not 50%. So thats one point disproven.
21 models compared to 35 (45 if it hits its maximum but it never will). 35 --> 21 is 60% of models (or 46% if ever maximised). That is not "barely less" but quite a bit less. So thats two points disproven.
MarkoV, personally I will trust maths over your superior win ratio. Warhammer is based on maths and tactical skill. Like I've said, I don't think the Mortar is the best unit to take, I do think it lies down there in the bottom half of effectiveness per point. However, it isn't all doom and gloom as some people think.
In addition, T3 units the Mortar is better. T4 the Rock Lobber is better. T5 or higher, the Mortar is better. They will be both be wounding on 6+, and even if you ignore the additional models the Mortar will hit as T5 units will be smaller, the Armour Piercing of the Mortar gives it the win. Rock Lobber only wins against T4 and Monsters (due to higher centre hole and wounds).
I'll look into the Rocket Battery now.
Edit: The Helstorm does look good on paper. The AP gives it the edge over the Rock Lobber - and therefore the Mortar on T4. T3 it would cause 10.5 wounds, which is lower than the Mortar. However, the Helstorm *could* launch more rockets. However, it is less likely to be accurate and get that full hit. Remember, a small target only needs to scatter by 4 inch to miss the unit (obviously, this is worse cause scenario). I'm not going to attempt to work out the likelihood it will miss/models it will hit as that way lies only insanity. However, yes the Helstorm has the potential to kill more models, but I never said the Mortar was our best piece of artillery.