I don't think that WC3 heroes would change SC2 much from SC1. They had heroes in almost every single player mission.

I never saw Starcraft as battles between huge armies. More often than not I would build groups of five or six units on hit and run missions. Rarely did I make armies larger than 20 units. Warcraft 2 was more about building huge groups of Ogres or Dragons and sending them into massive battles. Warcraft 3 turned into a game of micro-management without much complaint.