I think: You need (very) hard drills, because Teixeira was a 6* player. My test was with 5* (98%) 18.y.o "good" fast trainer.
The main question isn't "how fast can I develop my player" but "How can I use less greens to develop my player".
So, it doesn't matter if I used easy or hard drills but how many greens I spent comparing with the old version, for the same development of this player.

I also think, worldclass GK-Training makes a difference.
without doing any tests, I also believe that the new training improves more the GKs with those special drills.