The charts in the 80s were faulty. I mean, calling record stores and radio stations? What did you sell/spin this week? And it was even very different between early 80s (you could stay at #1 for two months) and late 80s (a new #1 every week). The best era was probably when they moved to SoundScan in the early 90s for some kind of accuracy.
But the biggest problem between then and now is: back then there was financial investment in a song. You had to release a physical single and sales of it helped determine chart position. If the record label spent $200,000 printing up 7"s and cassingles and CD5s, they had an investment in the song.
And if a radio station played a song, they risked losing their audience to another station because the song sucked. There was no way to track how many times people played a record/CD in their house. Hell, even MP3 sales at 99 cents was at least SOME kind of investment by the listener, even though it's easily manipulated by a record company - "we don't have to spend $200K printing up CD singles, we'll just buy our own song on MP3 10K times and watch it fly up the charts".
But this whole streaming thing is bullshit. No investment by record label or listeners. Charts are easily manipulated, like how I posted earlier about that Beiber single. He just sends out a tweet saying "stream for at least 30 seconds on this platform. stream the whole song here, put it on a playlist and loop the playlist. etc etc etc" Instructions on how to manipulate the chart direct to the fans. They didn't track how many times someone played a song on their walkman or boombox. But that's what they're doing now.
I see chart manipulation all the time. I'll have to start taking screenshots when I do. People in Facebook fan groups saying, "I created a playlist of the new album and put it on repeat. I'm probably up to 1,000 streams of each song!" Followed by "me too!" Broken chart!! Get off my lawn!!