This is my thoughts on the placement of the levels on the Demon list.
Erebus: Looks to be extremely high paced. Definitely above Yata but slightly harder than SW.
Sonic Wave: Tricky sections and hard timing with high paced wave. Could be interchangeable with Erebus.
Yata: Was really hard but got nerfed by TrusTa brutally. Not as difficult as Zaphkiel now that the latter is verified.
Zaphkiel: Very high paced level and seems nearly impossible on 60hz. I would place at third above Yata.
Artificial Ascent: Quite simple to memorize but fast paced. Would like to see at fourth above Yata and below Zaphkiel.