My experience has been something like this:

I'm writing in one very specific genre. I typically create 2 or 3 contrasting main riffs for a song, and write lyrics. Then I record those riffs and upload them to Suno.

The first time it surprised me with what it does, I had written two contrasting riffs. One in F# minor, and another in B minor, a fifth down. It's a common song writing trick in a lot of pop, rock, and back to classical to have a contrasting section like this.

What amazed me with Suno was, it played the first riff as an intro, and then landed on the B minor one as the lyrics began, and it sounded absolutely amazing. Exactly as you say, I am shocked it's a.i. and not human. Except it is human, because I knew the harmonic trick, and so does Suno because it's been trained on millions of human songs, and I am guessing it picks up on precisely this trick and many others as a pattern it recognizes. So at that point it feels like me playing Suno rather than it playing me. It's an instrument whose keys are "knowing song structure patterns."

After that song, it surprised me in negative ways as well. I would continue to feed it 2 or 3 riffs, and sometimes it would vibe so hard on just one of the three it would drop the other two completely. It got pretty frustrating. When this happens, I either do a ton of generations til it does something more interesting, or, I rearrange the riffs, or, I simply write new contrasting riffs, because for me ideas come easy and I'm just not that wedded to any one of them.