When someone talks about former top 1's, they usually mean demons that were once on the top of the Demonlist. However, demons are often over- or underrated on release due to insufficient opinions, or remain relatively unknown until later. I think it would be more accurate to judge the difficulty of top demons by their current, more accurate positions. Here's the list of former top 1's, according to the current Global List ranking:
Tartarus 2020.01.06 (#135)
Sonic Wave Infinity 2021.05.30 (#130)
Arcturus 2021.08.08 (#128)
Diabolic ClubStep 2021.09.01 (#122)
Firework 2021.10.30 (#60)
Slaughterhouse 2021.12.21 (#42)
Abyss of Darkness 2022.04.03 (#32)
Silent Clubstep 2022.07.18 (#20)
Tidal Wave 2023.09.10 (#7)
Thinking Space II 2025.05.25 (#4)
Society 2026.06.24 (#3)
Artemis 13 2026.09.10 (#2)
GRIEF 2026.10.05 (#1)
In particular, to our current knowledge, Acheron and Avernus were never actually top 1. Firework, despite being a "robbed top 1", was actually the second biggest difficulty jump in the game's history after Tidal Wave. Arcturus was the shortest-reigning top 1, holding the spot for 24 days; it is closely followed by Artemis 13 at 25 days.
What do you all think? Please let me know if I made any mistakes (which is likely).
P. S. I'm sorry if this has been done before, but I couldn't find any posts with the same idea, so I figured I could as well post this.
EDIT: Acheron was indeed harder in 2.1. However, The Hardest Achievements List currently places the 2.1 version below Anathema, which is currently #26 and easier than Silent Clubstep. Though there's also an opinion that Silent Clubstep's current position is inflated due to its bad gameplay.