The question is: Will hand weapon+shield warriors achieve anything?
And, while i agree that the points costs (of infernals, all their upgrades, ironsworn and bull centaurs and all their upgrades) are ridiculous, it may be the case of "not enough killing power" if you leave the infernals without great weapon. So, too expensive they may be, but i'd rather take overpriced great weapon wielders than a unit which is just not fit for today's warhammer battle field.
Of course, if the killing power comes from other units (but which?), then a stubborn center of "naked" infernals will be enough. I recon we'll see naked, great weapon and sometimes a smallish unit of fireglaives. Alternatively, leave the great weapons at home and invest another 2 points for ironsworn.... (who will at least have decent protection, a magic attack just in case as well as hitting before ironguts and the like.)
Thinking of it, WF really made a sneaky move: They offer no models with blunderbusses - they design shitty blunderbuss rules. The design no infernals with great weapons - they offer ironsworn as an alternative, for which they already have models. ;)
First, I played IG with Fireglaives for 7,5 Skaven Slaves each. They did pretty well, sometimes they were able to shoot down smaller units of cav, lone chars or something like fanatics. They mostly hit on 5s or 6s when they moved, which was already pretty poor for this point costs, but hence it was okay.
In CC they had S5. They stroke last most of the time, hit on 4 and wounded on 2s or 3s, which was fair as well. They never dished out the damage you expected they should, but overall, they weren´t bad.
Now, with 8,5 skaven slaves per model they are simply absolutly overpriced for what they do. Putting out some wounds at range and recieving +1S in CC is simply not worth the points.. 2,5 SS for the option to shoot is simply not cost effective anymore.
In my opinion, you´re better of with 20-30 HW/S IGs and invest the 100+ points you saved on them into a decent warmachine.. Which will kill more points than any IG with Fireglaive could. And don´t miss that S4 isn´t bad, especially when the regiment is tough as nails with 3+/6++ base. You won´t crush the opponent like a skullcracker or bull centaur does, but hey, you get the most out of that unit if you think of cost/effectiviness relations. Do not forget that with Metal magic you can give them +1 to hit in CC, armour piercing AND magical attacks or with lore of Hashut Hatred. Most times they will protect a char or two as well, which add another offensive boost to the unit. I´d use this unit as a bunker for chars, a point bunker and a medium elite unit that takes care of low-medium threats. They are totally fine for that, for example to deal with Black Guard or Ironbreakers or Chaoswarriors. Leave things like Hydras or Chosen to your other units and you´ll see they´ll do great.
Blunderbusses are totally out with 3 SS each. With 12" you will not kill anything if the enemy is mobile, and thus you need 20+ to make them work.. That´s 120+ points you´re better spending onto warmachines again..
Only real option are the GW, even if they are expensive. You loose some defensive gear, but become more offensive. Striking last don´t hurt them that much, but instead they gain S6, which is pretty impressive for a core unit. This way they can go toe on toe with harder foes, but of course you have to take some more models. Expect to recieve more kills due to only 4+ AS. The unit should have 5-10 additional models to compensate that. Of course, the more you take from them, the less points you have to spend on other choices, and CDs have great choices in special when you will notice you´re missing the points invested here! None the less, a good choice and I think it comes really down to your personal prefference whether you take HW/S or GW on them. Depends on your playstyle, but both options are good, even if the GW could be 1 point cheaper..
I think a unit with GW and say 20 men (7x3) with Infernal Castellan BSB could do real good, as they are stubborn on LD10 with reroll. This way you can keep them in "small" numbers so you don´t have to take many backup bodies. They can soak 7 wounds until they start to loose effectivity, that should be totally enough.
Instead a unit with HW/S and say 25 men (5x5 or 6x4) could form a very decent anvil, especially if they carry a Daemonsmith with S5 bonus and metal magic support. Sure, they won´t do as much kills as the GW unit, but they will take less wounds in return, which should turn out the same results in return.
Personally, the targets the GW are meant for, I´d rather try to shoot or to splash with bull centaures, a Iron Daemon/Skullcracker or a Kdaii Destroyer ;) But thats just me.
My 5cents so far.
Try to take a character with the Ironcurse Icon, for 5 points it will save you around 50 points per battle, sometimes even more if you face empire or dwarves.