Harmonic similarities between Tocatta from L'Orpheo and Das Rheingold, Prelude to Act I

To me, at first glance, the prelude to Das Rheingold's first act and the Toccata weren't very similar. I was prepared to talk about the thematic difference between the two, one being a Tocatta, fast and virtuosic, and the Prelude being more pensive and tranquil, but upon further listening, I found that they do actually share something very foundational. They're entirely based on and inside the tonic triad. I first noticed this in Das Rheingold's horns. To be fair, I might be stretching this since the piece is in Eb Major but I believe it is borrowing from the tonic of its relative minor. After the arpeggio section in the horns, I believe that melody and harmonies remain inside the tonic triad. L'Orpheo remains melodically inside the tonic triad and all the other instruments switch between playing the Tonic and Dominant with various rhythmic differences.