My pre-pandemic experience of Illuminations was that it was always crowded. And even if that represented a smaller crowd than before... that took decades.To be fair, Illuminations crowds waned through the years also. On our trips 2011, 2014 and 2017, we could walk up and get perfect spots as it was starting. No people waiting around for it and no huge crowds like we used to see.
On the flip-side, seeing Harmonious was not a priority for us on our last trip. I suspect we will see it more next trip as staying in Epcot area.
Harmonious will never live up to Illuminations though, just based on the music alone. Nothing can top the Reflections of Earth music. I love it still.
For Harmonious to be (in my experience of this past December and May) lightly attended in just a year (in comparison to Illumination pre-pandemic), it's a sign of not being a repeat must-do, like Illuminations was for so many (and HEA had become).