some yes and some no. The best player i ever saw used 21 and a little and it wasn't a little. Reyes also plays way north of 21 ozs.
Advantages?
Shorter slower stroke. Because mass x velocity sqaured means nothing when it comes to consistancy and pure straight aiming.
Slower cueball speed means more spinn with less effort.
This allows for shots not possable with a lighter cue.
The great eqaulizers are fast cloth and soft layered tips. These allow for a lesser advantage with the heavier equipment.
The big deal is especially with a scruggs or cochran is they feel 2 ozs. Lighter than they really are when you lay down to stroke!
Light cues have less squirt especially with soft layered tipsand thin shafts.
The new equipment allows for position play that was impossable on the old cloth. It has taken most of the skill out of the game. And with that the light cues are not a disability.
There are advantages for both. I wish everyone went back to the old cloth. You would see world champs crying about they can't run 100 like they used to. Probably break the ferrules on their light cues trying to follow the ball.
They would even have to change how they address their shots. This fast cloth is like playing from the lady's tees.
Nick