A big downside to the Fyreslayers is the lack of choices for units. Also, that they’re not sky pirates. Splashing in some Kharadron Overlord allies solves both problems.
Skywarden (volleygun) 
Skywarden (skypike) 
Skywarden (drill cannon)
As these guys are steampunk, there’s obviously a lot of metal. But I also pulled in the reds and greens so they belong with the Fyreslayers.