Thanks for posting your painted Blackstone minis, I was anxiously waiting for the first batches to start coming in. You bring up an interesting point about the scale creep, and I'm not surprised to see it with the Eldar. I was expecting to see the same with the Kroot model I picked up, and it does follow the same pattern.
I think it's likely the heroes are larger for the game, and not a representation of what may happen in the future with larger releases.