Ah. Okay, I see where you're coming from.
I completely agree that Warrior/Termie is a monster support formation.
I mostly agree about Hormies. They have limited use. I use a few because they are cheap meat shields (meat-shielding Termagants - heh

) and they help ward off CC assaults that try to take advantage of the Termie weakness. The other use is to recycle the meat shields as spawns once the enemy is close. They can Engage 40cm from their spawn point at 4+ rather than 30cm at 5+ for Termies. Not completely useless but I still wouldn't take more than a handful.
The point I would disagree on is the "never engage" conclusion. I think gaunts can make a fine assault late in the game when they get in range and most formations are chewed up. Half kills might still be okay here, but it could be a problem.
What are the other consequences?
If gaunts only count half in assault, why would anyone ever take Raveners? A Termagant in assault would have the same FF fire and only count as 1/2 kill per hit versus a Ravener's 2/3 kill per hit (failed armor saves). Raveners are basically only functional as offensive assault troops anyway because on defense in assault or against ranged fire the likelihood of cover saves is pretty good. Not an over-powered problem, but still a problem.
What happens to the relative strength of a Dom that's trudged across the board and slowly spawned 4 or 8 over a couple turns? Perhaps it's not common enough to matter, but it is something to consider.
Same question for a Harridan or Vituperator. It's a common tactic around here for them to move to a prep position, spawn disposable broods and assault in the following turn. Half kills makes that tactic considerably better. I actually see this being a bit of a problem.
Last on for now, half kills is a very large boost for a full on "horde of gaunts" army. No one's done a batrep with one in a long time, but last time I looked they did work. That's a potential major problem.