"We know that long term muscle memory for corner activation is just as good as the edge approach."
You seem to be forgetting that accessing an icon launcher is a two-phase approach:
1 - revealing the launcher
2 - going to the icon
Your assumption above is valid for (1) but not for (2), because (2) does not benefit from Fitt's law and thus distance matters. Imagine a user with a large monitor wanting to access the Trash.