There is a hidden parameter (Talent) that determines the pace of training; the higher this parameter, the higher the Value. Nothing less, nothing more.
We just agree to call players with high Talent "fast trainers", but there is no specific flag of "fast-trainer-ness" nor grades of it in the game mechanics
AFAIK. We can add grades artificially, but I honestly don't see the point.
"Second freshness - that's what is nonsense! There is only one freshness - the first - and it is also the last. And if sturgeon is of the second freshness, that means it is simply rotten." (Bulgakov, "The Master and Margarita")