Exploit or feature?

[Toxcatl]

Are you come in peace or we should look for a shelter ?

hmm, you mean (in human language) that GK training gives more gaining to a ST than the Wing Play drill ?

Not by itself. GKT is unique among other drills. It gives raw undistributed experience to field players, and this experience goes to skills only on the next drill (if it's not GKT again, otherwise it just accumulates).
If the level of GKT is higher than level of Wing Play, then [GK Training + Wing Play] give to ST more than [Wing Play + Wing Play].
The more GKT you insert before Wing Play (any lower level drill in fact), the more will be the difference.
And if it's not enough, do like this:
6x GKT
6x GKT
...
5x GKT + [any other lower level drill]
It's even better =]

This raw experience from GKT dissapears before a game if left undistributed.

Have I discovered America here? Do I deserve a candy? =]