90% seems high, of course I've never spent any time analyzing MMORPG chance tables.
Well, that being the case:
1. Do defensive buffs/gear affect that greatly?
2. Is the probability range on low damage hits MUCH higher than high damage hits? Surely it is...
90% base change to hit equal level targets. Higher level targets start dropping your base chance. And lower level increase it slightly.
That is just you base chance, but there are modifiers on top that can reduce and increase. Your targets parry and deflection stats all decrease that base chance to hit by their percentage. I'm not sure if it is a percentage off or a subtractive percentage as there is no combat logs to verify. For example, I have a skill called Force Breach which is suppose to lower the target's accuracy by 5%. So I'm not sure if their base accuracy drops from 90% to 85%, which is subtractive, or if it drops from 90% to 85.5% (which is 5% off 90%). The difference in that regard is so hard to tell even if there were combat logs. I also have another skill called deflection which increases my deflection rate to 50% for 12 seconds. Again, I'm not sure if that puts the target at 45% or 40% accuracy. Either way I can most certainly tell my character is deflecting attacks like crazy at that point.
The base chance to hit only goes for melee and ranged weapon attacks. Spell like abilities use resistances to determine whether they go off or not.
But everything is die roll. If you have your target selected, are within range, have line of sight on them, and press the button the ability will go off on them. There is no aiming. A die roll determines success and the base success rate is quite high.