I've decided to cut out the math bits, put them into a separate entry and just give the results in order not to dilute the text too much. None of the spoilers are essential, these are just some thoughts for specific units that I tried to keep as general as possible.
Stormfiends and Acolytes are bad investments without buffs, in particular MMMWP + Spark. Jezzails are decent without buffs. Doomwheels are a utility piece. Warpfire Throwers and Cannons have their niche. Give Ratling Guns a chance.
What does "100 pt efficiency" mean? "Average damage" of what? "Compensated for overload" ?
If you spend a 100 points on a unit, how much damage can you expect on average. A way to compare units with different costs.
Average in the most colloquial of all senses, per whatever smallest denomination you can buy. E.g. what is the arithmetic mean of a unit of 5 Acolytes over the course of their careers slinging poison?
For units that have a clear chance to die when overloaded it took the chance, multiplied it with the cost and added this in order to better illustrate the "true" cost of the unit. Essentially some optional information.
Warp Lightning Cannon: (180 pt, 24 + 3")
avg dam 100 pt efficiency
Base 3.5 1.9
+Overloaded 7 3.9
+ Arkhspark 8.7 4.8
~12 % chance to blow itself up on the first overload. Very likely on the second. 89% chance to take some damage when overloading.
The average here is relatively meaningless since it is the average of six equally likely scenarios, depending on which number you rolled on the first attempt.
WLC has a niche for taking down ethereal high value targets (e.g. 3+ Mawcrusher with ethereal amulet) or sniping support targets since it can neither be buffed nor debuffed. It does nothing really reliably but you will rarely roll dice with as much tension as with this happy little camper.
Jezzails: (140 pt for 3, 30 + 6", vs 4+ AR)
avg dam 100 pt efficiency
Base 3.2 2.3
+ Spark 4 2.9
+ re wound 4.8 3.4
Sending them through a Gnawhole is a setup, not a move, so they retain their re-roll to hits. This can be used to either keep them safe if there is a counter to them on the field or extend their range.
3 Jezzails do 1.5 of their damage as mortal wounds, assuming re-roll to hit and 4+ to hit.
Since they are not all that reliant on buffs - compared to other units - they can be part of any list, even in sizes of 3 or 6. The most common size is 9 to fulfill your long range needs and support your army in that way. A unit of 12 has the advantage that it can shoot monsters like keepers or bloodthirsters off the board in 1 turn with over 90 % accuracy, compared to the 50-50 chance you get with 9.
Stormfiends: (260 pt for 3, 24 + 6", vs 4+ AR, ranged variant, mid-range of 10.5 shots for ratlings, target for Launchers < 10 models)
avg Launcher avg Ratling 100 pt efficiency
Base 1.5 2.3 1.5
+ Spark 2.3 4.6 2.7
+ re hit 3.4 7 4
+ re wound 5.1 9.3 5.5
+ Vigordust 6 11.1 6.6
Ratling Guns are the real breadwinners for this unit which is why SF lists tend to need a plan to get them into range. Commonly this means a Grinder or Soulscream Bridge.
A unit of 3 is only really seen in a warpfire-short range variant. For the full ranged experience take 6 in a mixed list, 9 in a skewed list.
Since MMMWP + Spark is so important to this unit, plan redundancy with two engineers or a tanky Arch-Warlock (Verminous Valour, Ignax's Scales, etc). Deranged Inventor is a solid back up plan when MMMWP fails.
Acolytes (60pt for 5, 6 + run + 8", vs 4+ AR, target < 10 models)
avg dam 100 pt efficiency
Base 2.1 3.5
+ Spark 3.1 5.2
+ re hit 4.7 7.8
+ re wound 7 11.7
+ Vigordust 8.3 13.8
Unless you take them as battleline in a Skryre 1 drop army, don't take them in conjunction with Stormfiends. Both desperately need MMMWP.
In order to survive the damage the enemy and engineers do to them, a unit of at least 15 is advisable. They come on 32mm bases so 30 man units might be a bit unhandy.
Ratling Guns (60pt, 6 + 12", vs 4+ AR, mid range of 7 shots, everything overloaded)
avg dam 100 pt efficiency (compensated for overload)
Base 3.1 5.2 (4.4)
+ Spark 6.2 10.3 (8.8)
+ re hit 9.3 15.5 (13.3)
+ re wound 12.4 20.7 (17.7)
This unit embodies everything clan Skryre stands for: teamwork, potential and beauty.
You can handle randomness in two ways: either don't rely on the source but use it to fill out your list, or double down on the randomness. 3 Ratlings give 6d6 x 2 shots, this means that you have a 90% chance to get at least 32 shots. The more you invest in randomness, the less likely truly horrific results are.
1/6 chance to overload on a unit this cheap is pretty much always worth it.
Doomwheel (160pt, 4d6 movement, vs 4+ AR, everything overloaded, mid range of 7 shots)
avg dam melee 100 pt efficiency (only ranged)
Base 4.1 1.3 2.6
+ Spark 6.2 1.3 3.9
+ re hit 8.3 1.3 5.2
+ re wound 11.9 2.7 7.4
4d6 movement will give 90% of the time 9 - 19", 66% of the time 11-17".
Overload chance of 1/6. Kills the unit outright 42% of the time.
I've seen a few battle reports recently where the Wheel was pushed straight forward turn 1 to shoot at chaff. Don't. Wheels are not Fiends, they don't just explode whatever is in front of them. At least place or teleport them to the flanks so there is an opportunity cost for the opponent when he sends something to pin it down.
Their function can be pretty much whatever you need and the enemy allows. I believe however that it's main function is distraction and slowing down advances, at least for ranged builds.
Warpfire (70pt, 6 + 8")
base overloaded 100 pt efficiency/ overloaded (compensated)
vs 3 1.5 3 2.1 / 3.2
5 2.5 5 3.6 / 5.4
10 5 10 7.2 / 10.8
15 7.5 15 10.7 / 16.1
20 targets 10 20 14.3 / 21.5
1/3 chance to overload. Gave this table for the sake of completion. Unsurprisingly it is good against many, bad against few models.