It's not acting lame. Overdrive in Warrior fills in proportion based on how much MAXIMUM damage you can do. Say at 150 Strength, you deal 99999 to a Dingo, you will receive the full recharge, since that is the MAX you do.

If your stats were at 255, then you are NOT doing the MAX you can do, because all attacks cap off at 99999, and therefore, the Overdrive bar fills slower.