It seems that at 25% it won't be really useful.
As far as I understand, 25% means that for trade routes will give 1 food and 1 hammer in proportion of 1 to 4 commerce.
If you have a trade route giving you 4 commerce, then you'll also recieve 1 hammer and 1 food.
Considering that in the game, if you trade with foreign nations, you can go up to 12 commerce/trade route approx (which would mean 3 hammers and food for EACH trade route of this value or more); it seems more than enough.
Percentages below 20% are the ones that are nearly useless and 15% only gives you some hammers and food in late game for routes of 9 commerce income or more.
Well, that may be possible by replacing Mahon. Or by making Kro'Mear neutral. I know MagisterCultuum think that Thessa should be a neutral Calabim but I'm unsure about doing that. However, if you have anything in mind, please, go ahead
Is there some kind of limit? I think Calabim have one more planned leader slot. I meant a new minor leader like others, with cool art that would make him/her look like a "lawful neutral" vampire; If you can.
Kro'mear seems like a greedy aristocrat accustomed to luxury and feasts, does not compute with neutral.
Also, I'm completelly against a leader being available to several civs. Decius, at least from the picture, is completelly unfit for both Malakim and Calabim and has a clear Bannor look. No matter how much backgroud is built up with scenarios, he will still be unfit unless he changes portraits and maybe traits according to which civ he's leading. In fact, Perp would do better as a leader of several civs

or some other crazy leader, maybe it is time for "Insane" trait to stop being Perps exclusive and make a "Chaotic Good/Neutral" flavoured leader with insane (A Lanun insane and crazy looking witch; Palgadee not since she's beautiful; like the one who appears in the Slumbering Coven part of the game in Neverwinter Nights 2 MOTB; Either way Palgadee could still fulfill the role with a cloned trait called "Dreamer" or something among the lines )
Pirate could always be a generic trait for sea tied civilizations. Still, only Lanun and Doviello (with Drakkars) have a clear "Pirate" and "Viking" flavour, respectivelly. Still there's no Doviello leader with sea flavour even when they have a Galley UU so maybe the last planned doviello leader slot could be used for this. Maybe a neutral leader with viking warlord looks "The one who would guide the doviello to new ice and tundra lands far away from Erebus" background.
Genious is powerful but not overpowered, in terms of commerce it would give no more than financial trait or the really overpowered Raiders is giving right now but with some tactical advantatge. The only problem is the religions eras but if this could be solved, it would give 3 techs. It can always be compensated with some drawback trait or by being a lone one with no second trait. Genious minor leaders could also start without minor trait
More trait ideas:
Diplomatic: +2 relationship points with all leaders.
Also, a whole traits "web" should be created with positive traits and negative traits.
Licentious: +1 unhelathiness in all cities. +4 relationships with other licentious leaders.
Conceited: -1 relationships with all other leaders.
Ravenous Harpy

: Females only. -2 relationships with other leaders. +3/gold city +1 unhappiness/city. Renamed from Greedy.
Manwhore: Males only. -1 relationships with males. +2 relationships with females.
Could be implemented via LeaderHeadsInfo but it would be better implemented as a dynamic trait easily given and mentioned in leader's pedia.
Jealous: -4 relationships towards the top ranked player; +4 relationships toward the bottom player.
Altruist: +2 relationships towards lower ranked leaders.
Ugly: -2 relationships with members of the opposite sex. Aplies to Mahon the Butched

and Weevyl, Pickle and Hide;. This, again, could be implemented via LeaderHeadsInfo.
Tolerant: Aside from the current benefits; no religious relationships penalty.
Peaceful: Aside from the current benefits; double relationships penalty from war declarations, double relationships bonuses from maintained peace.
Heroic Explorer (or Brave or Conquistador , or something among the lines) : All recon units start with Adventurer promotion. No it's not overpowered considering we have a trait that doubles pillage gold AND gives a high-ranked promotion to all units.
Topograph: All recon units start with Sentry1 promotion.
Relationships traits would need some DLL work (I guess specially Jealous and Altruist) and maybe are too hard to be implemeted but they would truly personalize a leader.
Also, maybe Gender should be applied via traits instead of leaderheads, it would be more practical as it would require less tags.
Etc...
I am suggesting to add new traits because there's a serious lack of them in your modmod. You added a lot of Leaders, and cool ones with good pictures; but the only real difference between them is the picture. You need to add more traits to compensate the this quantity if you really want to add them a personality.