" either an ASDFGH or ASDGHJ control scheme - having all the keys next to each other would make it easier to deal with notes very far apart as you wouldn't have to think about the gap in key locations"
Won't work since we have 4 really good fingers (since thumb reaching which fingers level is kinda weird feeling) this would eliminate the combo moves we could perform if we try the game one handed.
If we choose to play two handed the index fingers of both hands would rub against each other and would cause annoyance and missing of tiles by sometimes since the one of fingers could touch and make the other miss , this would be annoying.
SDFJKL is better for this since most keyboards have small notches that can be used for locating the keys in hurry. Hopefully this comment helps you to understand the design decision