That's all pretty much in line with the point that said that if you're training guys who aren't going to be cap-limited, having the elite level 7 trainer just gets them there faster. You specifically said from 50 TSP to 120, and that the extra 10% (your estimate which I am accepting for the discussion's sake) would put the level 7 guy at 127 instead, which is admittedly better. But the real benefit isn't a raw 7 skill points, but instead getting him to that 127 faster than the guy trained with the trainer that's 10% slower would take.
Now, if you're training elite absolute top of the line guys for international/B3 level play, there's a strong case to be made for the level 7 guy. I'm not going to bother to try to analyze the cost/benefit of that because I am certain you've done so and in your case at least determined it makes sense. I am just saying that there is no way that even 25000 users can train that level of elite player, and the number of people who should do so is far lower than the number who try.