On paper a full sleeve suit is always faster. More neoprene= more buoyancy+slicker scs coating= lower drag coefficient.
...At the same instant, the top arm is out of the water in its recovery phase.
...It seems that added buoyancy at this point is moot.
Exactly when during the stroke does the additional buoyancy from the arms benefit the swim?
First, "on paper" doesn't mean that it translates to actual performance.
Also, when do you have better glide? With a full sleeve wetsuit? or in the pool with no wetsuit? Personally I feel a much greater glide while "my top arm is out of the water in its recovery phase" with a wetsuit on. Granted this will be helped by the thick panel down the front of the suit, but the 1-2mm thick sleeve will also help to keep you planed out during the "recovery phase".
Keeping in mind that your stroke goes underwater, this thin sleeve will not create drag or slow your arm speed without benefit. A larger surface area pulls more water. Now you can say that the SCS coating negates this, but in comes the catch panel breaking up the water and helping you to have a much greater pull.
For the most part you are correct, this extra buoyancy isn't going to put you in the olympics, but it also is not enough to hinder your stroke rather it is just enough to help you lengthen your stroke and aid your pull.
This will vary from person to person, but again, this is how it should work.
Reference: USAT message on June 21st 2010
"...The adoption of this rule is designed to eliminate any competitive advantage gained by enhancements in wetsuit technology in recent years. Studies have shown there is a marked and measurable performance benefit to the use of certain wetsuits, specifically added buoyancy effectively reducing passive drag. These performance benefits have led to an increased, and artificially induced, reduction in physical demand required during the swim leg of a triathlon and an increase in speed."
From Desoto Water Rover:
- 8mm: Found only on the arms from the triceps to the wrists. This thickness creates a larger surface area with which to push water. The thick arms also create an additional level of surface buoyancy during the reach and glide phase of the swim stroke..."
So is the point moot? No. It is designed to be a performance enhancing feature on the wetsuit. Definitely separating a full sleeve and sleeveless.