I could see MC being added because the editor believed the young male audience wouldn't be able to relate enough to the gyaru to stick around. As it stands, MC serves no purpose in the story outside of that
Well, the MC, Hikaru, is the main character of the original YouTube web series that this is based on. His main role is to play the straight man and make commentary about the weird things around him. The gals were from the original web series too, and with this manga that's primarily focuses on the gals, Hikaru plays the same role that he did in the original, just he's not the main focus anymore. I've been
translating the original web series, so I recommend checking it out if you're interested!