There have been some slowdown issues reported on young NT hopefuls, and elsewhere in the forums. Here's a fine example from Astragoth: (199625.32)
Elastic effect. My then 22y old was popping just fine from 13 to 14 and from 14 to 15 in OD; pop every two weeks. However, he had DR 14 and HA 13.
Then again, for the first time in his "career", my U21 player needed 3 weeks for OD to pop (14 to 15). His DR and HA are both 13. But except for ID, he has low inside skills so maybe CT was bringing that down a bit. If CT had such a great effect like you are claiming to have from this example, my player should employ at least 4 weeks to pop in OD - and that's not the case.
I fail to see how you player is like the example Astragoth posted. His player didn't have a single skill within five levels of the one he was training, whereas yours had/has two skills within two levels of the skill in question, and both of those skills are secondary to the trained skill. I think you're comparing oranges and tangerines.
I don't claim to know anything about CT for certain, as I don't believe we've had enough time to experiment with it to have enough data to draw too many conclusions. But there have been posts like Astragoth's that suggest that, at very high levels, it makes sense to stop training something for a while until the player's other skills catch up.