spoilered some irrelevant stuff
[Spoiler]I wouldn't classify any of those four units as a skirmisher, myself. Spectre's completely different. Penetrator and Firewalker are expensive and have very low HP; they support your army but they are generally not its main body. Wolverine is cheaper and you can make an army out of them (plus some support) but they're terrible unless you have a large group of them.
Mistral is reasonably cheap and has merely mediocre HP/cost (unlike Penetrator/Firewalker) and it's still useful if you have only one or two (unlike Wolverine).
That being said...
Mistral having the range and speed properties it does makes it need to be weak in terms of DPS/cost and such, so perhaps this is just semantics. I think a better analogy is to a longer-range Scalpel. In the mirror I'm not sure you want all that many with the present numbers on the unit, but I speculate that you would probably make a lot of them against Hovers.
