Well... There's that gimmick, but that requires many, many turns in order to start paying off at all. In the meantime, you're still lagging behind everyone else as far as expansion is concerned because your nationals are mostly useless, or at least very glass-cannony (requiring more rest stops or expensive healing), and to top it off you can't even use your leader to help out because she (yes, it's a she) happens to be busy first stewarding and then researching.
Strongest Fire gimmick I've seen so far was just to take a warrior leader and give him the Dragonscale armor. If you're feeling particularly cheesy and have enough points, sell all his XP levels to buy the Eternal Flame.
From that point, you can take out almost every single neutral camp BY YOURSELF. This of course results in massive amounts of XP for the leader and also fame for your fame stockpile. The only camps that are troubling are various types of magic (both Chaos and Fire magicians have spells that spin around a fixed point and damage everything they touch, which is enough to break through your defenses. Death mages can just kill you outright with one particular spell).
There are much, much slower versions of this warrior-soloing strategy, including Earth warrior with the Obsidian Plate and a Death warrior with the Ebony Plate of the Void. Note that none of these strategies work particularly well with the autocombat, as they require certain tactical measures in order to work.