One interesting issue with conventional Mathhammer is the fact that the total cost for a unit tends to be taken into account for the firing of the main weapon. We tend to divide a unit's cost by the number of wounds it can deal to a single target to get "points per wound", but this often ignores secondary weapon systems a unit may have.
Here's a simple, crude way to get around this problem. Let's split mixed-role units into two "parts" so to speak- which we will treat at separate models for Mathhammer purposes. As an example I'll look at a Broadside with Heavy Rail Rifle and 2x SMS.
The Broadside's weapons, put together, cost 103 points. The HRR represents 61% of the total weapons cost, and the SMS 39%. Let's split the Broadside's base cost 61/39 as well. We end up with a partial base cost of 49 for the HRR "part" and a base cost of 31 for the SMS "part". In total, the anti-tank role of the Broadside is a 112-point investment while the anti-infantry role is a 71-point investment. With this in mind, let's run some points-efficiency numbers based on these new values:
HRR vs. Chimera: 2 shots > 1 hit > 0.67 wounds > 2.3 damage (47.3ppw)
SMS vs. Infantry: 8 shots > 4 hits > 2.67 wounds > 1.8 damage (39.4ppw)
HRR vs. Chimera: 2 shots > 1.17 hits > 0.78 wounds > 2.7 damage (41.5ppw)
SMS vs. Infantry: 8 shots > 4.67 hits > 3.11 wounds > 2.1 damage (33.8ppw)
HRR vs. Chimera: 2 shots > 1.56 hits > 1.04 wounds > 3.6 damage (30.8ppw)
SMS vs. Infantry: 8 shots > 6.22 hits > 4.15 wounds > 2.8 damage (25.4ppw)
Does this make the Broadside good? Not exactly, its actual damage output is still low. However, it helps us get a clearer picture of its overall capacities, and a method of figuring out the real inefficiencies of mixed-role units.