Allah sometimes gives reasons for the prohibition of some things like gambling:
Shaitan (Satan) wants only to excite enmity and hatred between you with intoxicants (alcoholic drinks) and gambling, and hinder you from the remembrance of Allah and from As-Salat (the prayer). So, will you not then abstain? (5:91)
But it has to be remembered that this is not the only or even the main reason we abstain from these things. The main reason is that Allah decreed them as sins and it is a test of our obedience:
They ask you (O Muhammad SAW) concerning alcoholic drink and gambling. Say: "In them is a great sin, and (some) benefit for men, but the sin of them is greater than their benefit." And they ask you what they ought to spend. Say: "That which is beyond your needs." Thus Allah makes clear to you His Laws in order that you may give thought."
In fact avoiding them is key to our success:
O you who believe! Intoxicants (all kinds of alcoholic drinks), gambling, Al-Ansab, and Al-Azlam (arrows for seeking luck or decision) are an abomination of Shaitan's (Satan) handiwork. So avoid (strictly all) that (abomination) in order that you may be successful.
So, in conclusion, we have to understand the main reason we avoid prohibited things and actions are not the rationale that is sometimes given, but rather it is because Allah decreed it to be forbidden. So, we don't do it.
An alternative way of showing you why it is still haram is this:
He who takes an oath in the course of which he says: By Lat (and al-'Uzza), he should say: There is no god but Allah; and that if anyone says to his friend:" Come and I will gamble with you," he should pay sadaqa. (Muslim)
Basically, calling someone to gamble with you is haram. So, even if for a second we accept your argument that since your chances are 90% and you worked for it gambling should be halal, you have to realize the implications of your chances of winning being 90%.
It means your opponents chances are only 10%, meaning he wouldn't have the same excuse you think you have. So what he is doing would definitely be considered gambling. Since you can't call someone to gamble with you and helping someone commit a sin is a sin, you can never play this game of you having 90% chance with anyone else non-sinfully (as you would be helping them commit the sin of gambling).