Talking About One Direction's new song and video "Best Song Ever"

First, I will talk about the song. It's a good song, good lyrics, instrumentals and voices, amazing! But once again Harry and Zayn or Zack :D, sang the whole song while Louis, Niall and Liam sang 2 phrases each other. That's not fair, I mean, I'm not a directioner and neither Louis, Niall and Liam's fan, but if they keep giving the whole song to Harry and Zayn, we will never discover what the other members are vocally capable to do. Harry has the lowest voice of the group  and he hit most of the "high notes" in the song, do they want to destroy his voice? Louis who has the higher voice of the group  stayed in the middle range, Niall whose voice is higher than Harry's stayed in the lowest range, and , maybe for the first time, Liam sang some high range of the song. Zayn was ok, he sang in his range.
Now let's talk about the video. I didn't understand what it was supposed to say to the viewers, was it talking about a boys band who want to stay what they are, or was it talking about a boys band who met their soulmates in a place where there was this song they named best song ever? I'm confused. The song talks about a guy who meets a girls in a disco, i don't know where, with a love song playing, but the video talks about something else. Please explain me :/