Vanguard/Powertech was the Fotm class for about a Year, and now it is just fine (maybe they nerfed it a little too much). Overall I think balance is quite good and never was better.
At no time was Powertech the best class. Sin was ALWAYS better, Mara was ALWAYS better. What powertech had was a counter to guard (doube dotting the guarded player and the player who was guarding). They had very good sustained dps and burst dps, but their defense as well as their utility was always lacking.