It would resist one spell, mages get three spells. I don't think that design was practical on its own merits. I do rather like the idea of expanding our metal faculties though.
I think that it is wrong to think of hunters as skirmishers, they have almost no range and very little resistance to ranged attack. Skirmishers are typically a ranged unit that can afford to get close to the lines. Hunters ought to be an opportunistic weapon primarily.
The sunk cost fallacy doesn't really apply. Sunk cost primarily applies to random events, where no value is accumulated. In the long run, the sentiment that creates the sunk cost fallacy can preserve resources. The line between the sunk cost fallacy and failing to ever finish anything is extremely thin, vague, and blurred. We have value, there are two good rolls in the hunter proposal, we did not have those rolls previously and there is a decent chance that even on a one our revision would provide a valuable outcome. We have not yet confirmed that a one on a revision means "no change in effectiveness" and even if it does, the odds of that are comfortably low and can be regarded as "outside of what we should be expecting"... The hunter has two design goals: To operate in forests and to move quickly. If we get it working well then we can get something to do to them what they did to us last turn, of attacking reinforcements, which ought to be much more effective given that we have the whole "hive mind" deal and a homogeneous army blob and they are busy trying to herd slaves disparate nationalities. I do not particularly like forest queens, but forest queens is what we got, so having something that can fight well in a forest would be helpful.
What we need right now is to expand south. We need siege weapons. We can hold the lines easily enough for now but we NEED to expand, and that means siege, because there are forts in our way and on the objectives. We do not have siege, and I do not believe that we can get siege with a revision, and even if we did, there would be precious little opportunity to correct any flaws in it. So second priority is to set ourselves up for forest queens, and we can do that now with hunters, so hunters are a good thing. We aren't just trying to recover our investment, we are trying to make use of the good rolls that we got. We are going to have many many designs that have one bad roll and need to be revised, to cry "sunk cost fallacy" at such things on principal will only result in losing the game. It is far too easy to treat things like codified fallacies as some sort of short-cut to proper arguments. It doesn't work. All arguments require understanding and name-dropping just doesn't provide that. Ergo, anyone who disagrees is Hitler.