I agree with Q. In base FFH (MNAI 2.5), both Luchuirp and Amurites are below-average civs. Both of them are potentially powerful in the late game (Amurites moreso than Luch) but they have to actually be able to survive into the late game. Luchuirp especially suck because they are slow and Tholal nerfed their worldspell--unnecessarily in my opinion--which was originally one of the best and now it's pretty mediocre.
I agree that Flauros/Calabim is the single strongest leader/civ in MNAI 2.5. In earlier versions of MNAI, Keelyn/Balseraphs was a contender as well. Problem with Flauros though is that he is weak until he makes it to Code of Laws--if you can't survive that long you can't leverage his strengths.
If someone put a gun to my head and said that I had one chance to win a game on Deity, I'd pick the Aggressive leader of Khazad. In MNAI 2.5 this is Kandros Fir. There are several reasons why Khazad are a good choice on Deity.
First, this is probably one of only two leaders that has a good chance of fighting off an early warrior rush before you are able to tech Education (the other is Tasunke using Warcry). You can make it to God King and build the Deruptus, which will give your aggressive dwarven warriors +2 xp, allowing them to start with Shock. Mass-produced shock warriors have a chance of fighting off a big stack of triple-promoted Deity AI troops if you can take favorable engagements, which will be easier for you to do thanks to the double-moves in hills you get from your dwarven race. Once you have cleared initial rushes, you can tech to bronze working and counterattack with experienced bronze axemen upgraded cheaply with Ingenuity.
The second Khazad advantage is that you have strong military options at multiple points in the game. I already mentioned the mass-produced Shock warriors pre-Apprenticeship, as well as the early swarm of bronze axes. Once you make it to construction, you get Trebuchets, which are the best early collateral in the game. If you can get enough production online, Trebs and bronze axes are probably enough to clear 2-3 civs off the map.
Even if the Trebuchet strategy doesn't work, Khazad have one last trump card up their sleeve in the form of Dwarven Druids. If you get contained, you can rush for Commune with Nature and get the game's strongest non-hero collateral damage. Since you aren't relying on a hero there is no chance that you'll be denied a key unit by the AI. Once you have a couple of DDs, you can go conquering with even mediocre troops as backup.
Finally, Khazad are rewarded for vertical expansion, so getting outsettled and choked by Deity AI isn't as harmful as it would be for other civs. Khazad can have a strong war machine going on only 3-4 cities. And you don't need that much anyway because you have such powerful collateral damage.
Other civs that have good chances on Deity:
Illians - worldspell, possibility of getting free aggressive from Letum Frigus, and 3 Priests of Winter at Priesthood give you excellent rush potential and rush defense. Even on Deity, if you make it to Priesthood you can probably take out one enemy civ.
Kuriotates - although they aren't militarily strong in the early game, they have a good chance of staying competitive in tech on even one city due to their powerful UBs. Once you get centaurs online you have a chance of taking out an enemy civ, due to strong production in the capital with Godking. Mid-game, if you can stay competitive in tech, you can summon Basium, completely offsetting your unique weaknesses and getting a Deity AI on your side.
Sidar - land is irrelevant for them, so getting boxed in isn't a big deal. You only need to get 1-2 wanes early to be competitive teching. Deity AI builds tons of troops, so that's just tons of potential xp for you. Problem is very early, your warriors don't have any advantages other than the free Homeland promotion, so you have to be very good with your tactics. Once you get Horse Archers it's GG.
Hippus with Tasunke - with Agg/Raiders and apprenticeship, your warriors can take Deity troops on head-to-head in the early game. Warcry is your trump card, use it to win a close battle in order to get some of your borderline warriors up to Combat III/March/Shock 2 level. Once you have these highly promoted warriors you can basically kill one enemy. Once you get horse archers, it's GG.
Lanun - Qgqqqqqq already mentioned them. They can stay competitive in tech, letting you leverage better units to win, and ocean commerce can't get pillaged by the AI early on. Drowned warriors are pretty good units. They can also rush Infernals out, giving you a chance to switch and have a big military advantage for a short time, even on Deity. Do a search for Horatius' Deity Infernals game to get a sense of how it works.
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Civs like Flauros/Calabim and Clan of Embers will be stronger than the civs mentioned above in the mid-game, but on Deity, the problem is usually surviving the very early game. Thanks to Tholal's work, the AI will attack ruthlessly if it detects any military weakness at all. If you want to win you have to have some strategy to deal with very early attacks, and the civs I mentioned are ones that have some trick up their sleeve to do just that.