If dragons had to describe their own power level progression, they would say that dragon power level progression was an improvement on their own natural talents and choices. Mages would say that dragon power level progression was a unique type of evolution determined by dragon genes… But, perhaps a more direct and vulgar description would be the most accurate.
"Go back to the womb and reforge yourself."
This was a choice that allowed for power level progression. Naturally, there would also be devolution attached to this choice that allowed for evolution.
For most dragons who fought after progressing in power level, the dragon would be like a completely different dragon. However, most dragons would take already predetermined paths for progressing in power level.
"What type of evolution will Little Red choose for herself?"
Even without having to ask her, I could faintly guess that it would be related to her personal talents.