Some Pretty Nice stats there Hong!. I've found the Swordsage to be a fairly balanced class. I DM for one that is 15th level and 3rd Level.
The Swordsage has not been at neither level the dominant combatant.
Manuever selection can play a key role in how the Swordsage plays.
The 15th level Swordsage/Master of Nine seems to be primarily focused on the Burning Wind and Devoted Spirit chain. I do know that he chose a maneuver from every school to maximize the bonus from Master of Nine. Even with that, I can not say he out damaged any of the other warrior combatants.
Where the Swordsage did prove useful was in the Tactical Arena.
The battle was a gigantic affair, played over 3 real days, probably a total of 18 hours on a single battle. The healing power of Devoted Spirit coupled with the ranged and Flaming Square powers of Burning Wind, coupled with Evasion, and some of the defensive swift DR granting powers of Stone Dragon School, and the character was pretty durable, despite having lesser HP.
In all a nice team player, however the Swordsage depends upon the player to utilize the correct power at the correct time, and like a sorcerer that has the wrong spells known in a circumstance, can be little more than an observer.
The 3rd level Swordsage seems to be specializing in Shadow Hand and Stone Dragon Maneuvers, which are proving to be especially useful. The Shadow Hand stance that grants you concealment after moving 10' is particularly useful, especially when conjoined with the Stone Dragon boost that gives DR 5- for one round.
Allows a sneaky character to saunter up, strike, and survive the barrage that will come after the hit.