Brother, I think you're actually making a mountain out of a molehill of doubt.
Even if we take for granted that some people are born with inherent 'bad' qualities, why not also ask about people that are born in bad environments or those with disabilities. Aren't they also at a disadvantage?
If a guy was born in a house where drinking, gambling, doing zina, doing weed, stealing and raping were all the norm and this behaviour was passed on to him, it goes without saying that he would have to struggle to be a good muslim a lot more than someone that wasn't born in such an environment.
What of the guy that was born blind? How on Earth is he supposed to be a good muslim when he can't even see. Unfair? :skeleton:
No, brother. Allah is All Just. It's one of his attributes. It's not just a word we use in vain. We wholeheartedly accept and submit to it. If we accept Allah exists, if we accept Muhammad Sallalahu Alaihe Wasalam was his messenger, if we accept the Qura'an is true, then we owe it to ourselves to first and foremost
submit and accept that there must be something we do not know that is preventing us from understanding. It's illogical not to. Secondly, we ask Allah for refuge from the shaytan. He is real and will, along with his minions, misguide us. So it's important that you take refuge. Thirdly, ask Allah to guide you to a better understanding. Forthly, take practical measures and ask those that know (i.e. scholars) as commanded in the Qur'aan, upon coming across something that confuses.
Sorry for the tangent, but I felt it was important to remind you brother.
Coming back to the topic though, we are told:
1. Nobody is tested above what they can handle.
2. The more a person has to struggle to rectify his character and align himself to the standard set by Islam, the more he would be rewarded.
<-- In fact, this one sentence ought to be enough to answer your question. Given that this world is a temporary test and the real objective is the hearafter, these struggling people are being rewarded more than those that weren't born that way. Would you now conclude that the people who aren't struggling are treated unfair, since they presumably get less reward in the hearafter?
Allah has said there would be seven people in the shade of his throne on the day of judgement. One being the man who didn't give in to the seduction of a woman when she called him to immoral acts. Stop and give deep thought to that.
Just how difficult is it to avoid seduction for a man? Not easy at all. Imagine being next to a pretty lady in bed, just about to satiate your lust. She's all ready and waiting for you. Would you find it easy to just suddenly jolt back and walk away from the scene?
Even Prophet Muhammad Salllahu Alaihe Wasalam has said words to the effect that women are the biggest fitna (test) for men. Most men would find it difficult to walk away. Hence the reward on the day of judgement.
Another thing we're told is that if a person can't recite Arabic to read the Qur'aan properly, he is rewarded doubly whenever he recites. This is all due to the struggle he has to undertake. I hope this highlights the point that is being made, that despite our circumstance and abilities, it is the amount we struggle that ultimately of importance and one that bears fruit.
Further to the above, generally, people aren't born 'all good' and 'all bad'. There are many shades of gray. Just because a person has one negative attribute, doesn't mean he is wholly bad. Likewise, if a person has one good attribute, it doesn't mean he is wholly good.
In fact, being (apparently) good can open the doors to pride and we all know how bad khibr is. A person with even half a mustard seed of pride wouldn't be admitted to heaven.
What one person finds difficult would be relatively easy to avoid for someone else. It's not all set in stone either. People can change as they grow.
Another thing that comes to mind is that when a person
wholeheartedly repents and feels bad about sins that he has comitted, Allah forgives him and
turns all his bad deeds into good ones. So if a guy is prone to comitting sin due to something inherent in him, but repents sincerely, he would be gaining many rewards. Now how is that unfair?
Btw: the blind person is guaranteed jannah because of the difficult test Allah placed upon him.