It’s true that a song is often portrayed by the general public as a melody and lyrics and nothing more, but most people are also swayed by what they hear on a record or performance, ie, the voice, the arrangement, the instrumentation, the playing. A song is best defined as an entity that stands on its own, and that can be adapted to many styles and performances. A great song played badly on an out of tune piano and sung by a terrible singer is still a great song. Too many recordings (and prog recordings in particular, like the jazz era before) consist of arrangement, performance, instrumentation, and recording technique but no song (or little) at all.

There is a songwriting tradition stretching way back in time which gives form and meaning to the structures of a true song, which real writers tap into, while the best and inspirational writers add something new of their own.  The Beatles were the last great songwriters, which is ridiculous, given how long ago that was. The tradition they tapped into was Cole Porter, Gershwin, Carmichael etc etc. Bob Dylan tapped into a different tradition of songs, the folk tunes gathered by generations, but it was the same ethos. Both approaches gave form and structure and foundation to anything that was built upon them. It’s high time we had a new era of songwriters who can do the same thing. But I don’t see any sign of it here in these archives, only great musicians and wonderful recording techniques. Imagine a marriage of the two then you get some idea of what’s possible. Without an inspirational song as the heart of a track, there will always be a lack of ultimate quality. (IMO!).

This is a romantic notion, but what does "There is a songwriting tradition stretching way back in time which gives form and meaning to the structures of a true song" mean?

There is a difference between ‘riff-based’ and a song with a riff. “I Can’t Get No” is a song. “Whole Lotta Love” isn’t. A song isn’t so much about verse-chorus etc, it can be whatever it is, the stricture is to do with tradition and writing form, much the same as in the best formal poetry. That’s not to say that rules can’t be broken, or more accurately, challenged. As Rick Wakeman said so accurately, you have to know what to do so you can avoid doing it that way. Indeed, that’s almost obligatory if inspiration is to play a part. But a lyric sung over a riff in a melody that works for that line alone (or for individual lines at a time) does not constitute a song.

There’s nothing wrong with a riff or musical composition that isn’t a song. If it works, it works, but it’s a different approach, more akin to arrangement. Songs are more to do with creative writing skills than the music for its own sake. Composers often show a bias towards melody and arrangement at the expense of lyrics and song structure. Translate a few operas and you’ll see what I mean! The foreign language often hides a lot of sins.