I can second Gregory being a fire elementalist in the previous iteration ... not only was it mentioned in the CS, he actually used it against the vampire he killed. 
From Jack's description, I kind of got the impression that while it is possible to learn to use secondary element(s), it would be almost impossible to use those two together - so he'd be able to temporarily switch to using wind, but not really use wind and fire together?

I also recall a rather elaborate discussion about gunpowder and how it and its alternatives have been (on Earth) discovered many times throughout history (though people haven't always been certain what to do with them). And that no need to use magic to produce it is a rather strong advantage over flashdust and liquid fire. And how you don't really *need* an explosive that is more potent than gunpowder for handheld guns, anyway - as there already are powerful handguns which are quite idolized by media but actually quite despised by people who do target practice for sports because the damn things will sooner destroy your wrists than add anything to the gun's accuracy ... or even its ability to cause damage to targets. If a gun can take out an elephant, it certainly can take out a lohk (and if you have a weaker gun, don't aim at its forehead; it's face, eyes and throat are probably easier to penetrate).

But yeah ... I believe Jack said you cannot produce liquid fire without dedicated magic back then. 
((Edit: I also imagine keeping vials of liquid fire on your person for longer durations would be dangerous as all hell, even more so for a physical fighter. Just imagine if he fell or took an impact to the wrong region...))

((Is it a terrible idea to bring in a wildcard chaos deity? I am still tempted to.))