I agree. I used to know the physics for this, but that was some time ago, all that 'Mass X Acceleration' stuff Everyone knows that a coach(bus) hitting a wall will impact more force than a motorbike hitting a wall. So it is with the mass of the racket head. If you play with a lighter racket then you need to be able to accelerate the head more, which is possible due to the fact that it is lighter. The heavier head will be harder to move fast, but will not need to be acclerating as much to produce the same power. I prefer a 3U, slightly head heavy racket. I play with a 2U head heavy racket sometimes but find my intercepting ability at the net is reduced. I think it all comes down to preference, style of play and strength of wrist.
No all lighter rackets are better and neither are heavier rackets. To me, it all depends on one's style of playing. I tend to like 2U weight rackets as I can generate more power in smashing as an arm player. A lighter racket will be good for wrist player who twists a lot.