> Maybe more difficult to model (not sure tbh, but granted for the moment),

Two reasons. One, strong players are performing tree search, so you need to model their tree search process rather than a simple depth zero prediction. And two, there are far fewer high rated players so there is far less high quality training data. A lot of high rated games are also bullet, which aren’t as useful.

> but it's _far_ easier to generate training data for strong players via reinforcement learning approaches.

Can you say more about this?