>>714518319
If you have cards with "Specialty Training" it helps.
Basically Stamina cards will appear more often in Stamina training, etc

>>714501758
Have you tried the cards with a "Specialty Priority" trait? It gets you more consistency when training, aka Power cards will appear in Power training more often.

>>714429128
Cards with the "Specialty Priority" effect will typically appear in their favored type of training (aka a Stamina card with Specialty Priority means that the character will appear more consistently in Stamina Training).

It would be hard to have 5 of those, but if you have just a couple, it could help, especially if they're the same type of stat.