I'm not sure that it shifts the importance to production Gavin. That has always been important from what I read.

I've always been told that if a songwriter wanted to be taken seriously by music business people, their demos had to sound very good. Not just to give an idea of the song but deliver the song. To be taken seriously, people did not want to have to imagine how good your song might be. They wanted to hear how good it is.
I'm sure there were and are a lot of insider relationships worked out on pianos and guitars, but anything presented at arm's length needed to deliver a clear idea of the product. Or so, I've always believed.

What I think has changed is access to the tools.

As for pop music songwriting...consider Madonna? "Like A Virgin?" Those were not the golden days of song merit. The Weekend is, at the very least, that good.

https://soundcloud.com/sunset-poet-of-texas