I haven't played the first 2 chapters in 5 years so I couldn't tell you how difficult the bosses were other that I definitely struggled more with Jevil than anything in these new chapters, but when ranking the bosses in term of difficulty
>Jevil > Knight > Gerson > Shadow Mantle User > Jackestein > Titan > Tenna > Lalino and Elnina (1st battle) > Roulxs + Weather Couple > Mike > Shuttah > Sound of Justice