I picked thief because I thought it would be an evasion build, but I was stuck with low stats besides perception and agility, so I could see where I was going and still fail half my agility ability checks to dodge harpies. Agility needs a damage buff, or a more clear way to use it effectively.

Thief is a best class arguably. I usually ignore Charisma and Magic and make Agility 8+Strength 5+Endurance 5+Perception 5. I buy a weapon like Broadsword, and I demolish everything because Agility plays role in determining many skills effectiveness (when the skill has When you're faster than the enemy requirement, it means higher Agility then theirs).

Overall, class is not determining your build effectiveness. You can add more stats through perk points and Achievements points. No class locks you from raising stats you really needed.