I've been reading through the Sympathy trait rules from Realms of Power: Faerie as some of my players (and myself) are interested in taking virtues and flaws that involve them. I'm quite confused by several aspects of them, because if I'm reading correctly many of the virtues and flaws would be either extremely overpowered or underpowered, and I'm wondering if I've misunderstood something.
As I understand it, gaining a sympathy trait in the first place "usually" requires a virtue or flaw, or faerie warping. Once you have a sympathy trait, you can practice with it, gaining 5xp per season. It increases like an ability, to a maximum value equal to your warping score. If your trait is negative, practicing reduces the absolute value of the trait, i.e. brings it closer to 0. Once the trait reaches 0, you can continue increasing it (per the errata on increasing sympathy traits).
Thus, it is possible to remove a -1 sympathy trait (a minor flaw) with just two seasons of practice, and turn it into a +1 sympathy trait (a good thing) with one more season. You need a warping score of 1 to do this. A -3 sympathy trait (a major flaw) can be turned into a +1 trait with 10 seasons practice, provided you have 3 warping. This requires no particular investment beyond the time available. These seem very small amounts of effort to get rid of a flaw, much less turn it into a positive. It would also lead to odd results, like having a positive sympathy toward iron. Is this actually correct?
Faerie sympathies can also increase and decrease as a consequence of die rolls. Rolling a 1 on a stress die modified by the trait grants 1xp, even if your sympathy trait is greater than your warping. Botching a stress die modified by the trait loses you one xp. The text then says that "these effects are reversed for negative Traits, so that a botch increases the penalty and a 1 decreases it". This doesn't seem to be a reversal at all: gaining xp in a negative trait reduces the penalty. So I'm confused what's meant to happen here.
Finally, if you have a negative sympathy trait, it appears that you not only take the penalty to all relevant rolls, but gain additional botch dice equal to the penalty on all rolls? This makes a negative trait really bad if you aren't able to get rid of it. This would seem to make a player even more incentivised to practice for a while until they turn the negative trait into a positive.
One little detail you seem to have missed is that if you start with the Major Flaw Faerie Antipathy, the starting score of the sympathy is -(3+warping score). Meaning that you have to increase your warping score by 4 before you can even start improving the sympathy trait with training or practice. (Change the 3 to a 1 for the minor version of the flaw)
(Your warping score needs to exceed the absolute value of a negative sympathy trait before you can improve it by practice, so you need a warping score of 2 before you can improve a -1 trait, and score of 4 for a -3 trait)
So, getting rid of negative traits usually requires that you get a bunch of warping first. Which take time, and often creates problems.
It's an easy thing to think of sympathies and antipathies as negative values of each other but it's probably better to think of them each as opposing positive values because there is no such thing as gaining negative xp merely gaining or losing xp.
For a positive sympathy, you gain xp on a roll of 1, and lose xp on a botch. The text says that for antipathies, "These effects are reversed: a botch increases the penalty and a 1 decreases it". In normal English usage, decreasing the penalty would mean suffering a less severe penalty, i.e.the antipathy is getting closer to 0. But gaining xp in an antipathy moves it closer to 0, so this would mean that you should gain xp on a roll of 1. Similarly, for botching to "increase the penalty" it would need to decrease your xp.
That's exactly what happens with a positive sympathy too - a roll of 1 gives you xp, and a botch takes it away again. But the text says that the effects are "reversed" for an antipathy. So either I've misunderstood something, or the rules contradict themselves.
For a normal (positive) sympathy trait, rolling a 1 gives you an xp, moving away from a score of 0. Rolling a 0 for a botch makes you lose an xp, moving towards a score of 0.
For negative traits the direction is reversed. Rolling a 1 gives you an xp, moving you towards a score of 0, while rolling a 0 on a botch moves you away from 0, losing an xp.
As for experience, the text is poorly written but the meaning seems clear: a botch always gives you "bad" xp, a 1 or practice always "good" xp. Sympathy is increased by "good" xp, and decreased by "bad" xp; this is reversed for Antipathy.
A character gaining via experience Sympathy for something that was initially his bane might feel "weird", but think of it this way: the character has fought the bane long and hard enough that he's actually mastered it, way better than the average person. This is an archetypal myth dynamic, in fact.
As for game balance, you are right: an Antipathy can be a devastating Flaw for most characters ... but this is balanced by the fact it generally does not last long: either a character quickly gets rid of it, or it quickly gets rid of the character!