A real master hasn't just captured nearly every Pokemon, but has worked with them and fought against them, to learn their strengths and weaknesses. The Pokemon Master knows the best strategies, but can also change it up on the fly to take advantage of any situation. A master can adapt to anything, and overcome anything.
The concept of a Pokemon Master became more and more unreasonable as the generations went on the and the number of Pokemon skyrocketed... but the reality is, we are the trainers who learn the new Pokemon, while retaining familiarity with the old. We are the ones that set out to catch 'em all. We battle, and learn, and grow stronger. Pokemon can evolve, but we are always evolving.
There are no Pokemon Masters in the game world. WE are the Pokemon Masters. Fact.
Nope, 8 year olds and nostalgia college kids who only play the game AREN'T pokemon masters. Beating up AI can be done by any child. Real pokemon masters are strong competitive players who play in tournaments. Otherwise any baby and their grandma is a "pokemon master"