In real life, different people learn in different ways. Some people learn best by reading, others by listening, some through tactile learning, and so on.
In game, pokemon have different personalities ("natures"). It'd make sense that some pokemon would evolve faster when trained one way as opposed to another.

So let me introduce an idea: hitting.

I think for gen 8 and beyond, players should be allowed to hit their pokemon. Of course, repeatedly hitting their pokemon wantonly would never lead to desirable results. Over-hitting would just cause resentment and the pokemon intentionally underperforming out of spite.
Then again, under-hitting pokemon would have the opposite problem in turn. Pokemon who weren't hit enough during or after training would grow soft and/or undisciplined. They might perform beneath their potential unknowingly or just doubt the authority of their owner.

Beating would have to be consistent and regular for the best results. The hardiness of a mon would dictate the method used for administering pain. Since weak pokemon like weedles and caterpies would be bare and receptive, it'd be best to apply hurt via a bare hand or light wire. Armored pokemon like shellder would require something significantly more intensive like a whip or a crop.

Perhaps there could be two groups of villains who demonstrate the wrong levels of hitting. For those that over-hit, we can use the placeholder Vicks (after that sports dude) and under-hitters could be called Coddlers. Vicks' pokemon are not at their best because they spite their owners and are weaken by the treatment, showing this method to be ineffective. Coddlers' pokemon are soft little shits who can't fight to save their life and crumble to pokemon well beneath their level.
Part of the story would be merging these two groups and showing how to effectively use hitting to make your pokemon true and earnest champions.