Again: Albanians of struga, ohrid and manastir (bitola) speaks tosk dialect. These areas are further south via egnatia. Check if you don't believe me. That area was always tosk, since the ancient times.
The arberesh of Italy are migrants of south Greece, who migrated there altogether with the Greeks onward the ottoman invasion. Their dialect is clearly tosk. The arvanites speaks tosk, but that dialect is more close to the cham-tosk dialect, not to the other subgroups of the tosk. Some gheg tribes migrated whether throughout epirus and mainland Greece, but that's all. Indeed they have been assimilated by the rest of populace. Linguistically is proven as far as I know, that the split is too old. I'm just asking you: why everything further north via egnatia is gheg! Don't forget, that during the Roman empire it was a gap. That imperial road was protected strictly by the legionares. I am not denying that ghegs migrated further south, instead I am saying that there was always a migration from North into south since the ancient times, but this migration didn't change the core of tosk dialect.