I will share my example with Goalkeeper drills. I have tested three players, and for me, they all gained same amount of skill points regardless of what drills I used - goalkeeper or other drills. And btw I have max training level. But here is very interesting other observation: some players get equal or almost equal amount of skill after goalkeeper drills. For example, my ML was trained with 6xGoalkeeper drills for around 10 times, then when I train him with fast counter attacks - he got something like 8 skill point in three skill, and 7 skill point in one skill. BUT, very interesting happened with my CDM, here is the picture:

Click image for larger version.  Name: MUSTAFI.jpg  Views: 67  Size: 47.4 KB  ID: 85538



He got twice as many skills in passing, then shooting or speed. I repeated the process and got the same result. Now, here are my two questions:
1. Is it going to happen in the same manner If I were to use only pass, shoot & go drills? If were not using goalkeeper drills would my CDM gain passing twice as fast as shooting or speed? I have not tested this yet, but I will only next season.
2. Does this mean that "white" skills train twice as faster as other skill? So it would mean that we have to concentrate on main skill while power training players?

Just for information, here is how Mustafi's skills look like:
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