I think Will, Rachel, and Finn were all protagonist and at different levels, Sue. (OTT everyone antagonist) Quinn and Puck were supposed to be their antagonist that first season. Other lessor antagonists were incorporated via Sandy Reyerson, Coach Tanaka and guest like Neil Patrick Harris. The leads were clearly marked in the pilot. Will represented the adults, Rachel the outcast and Finn the popular kids. I think they needed that balance of the 3 leads but did switch more towards Rachel and Finn in season 2/3 and Rachel after Finn passed away and the new kid did not take hold. Will did have a bit of a surge in season 6.