For context, all bosses are being played on New Game Plus (or hard for Asylum), and that's how I ranked them. Leave your own list and tell me just why I'm wrong in the comments.
And, for supposed bosses that didn't appear on the list, here's your explanations:
DLC Bosses: I don't have every piece of DLC, and it would be unfair to rank some but not others.
Zsasz (Asylum and City): Zsasz in Asylum could be replaced by a basic thug and have nothing change. And Zsasz in City doesn't affect the terrain of his final encounter like Mad Hatter and Scarecrow.
Harley Quinn (Asylum): You don't fight Quinn and she doesn't impact the fight enough to count.
Riddler (City): Same as Zsasz, he doesn't actively affect the terrain enough for me to count it.
Electrocutioner (Origins): He could be replaced with a basic thug, since it only takes one hit to defeat him. I really wanted to, but I couldn't break my own rules.
Black Mask (Origins): Doesn't have a health bar and acts like a regular enemy the whole time. Plus, when I tried getting footage of him, he seriously glitched out, so yeah.
Joker (Origins): It's an interactive cutscene. You just spam the punch button and occasionally counter. I love the sequence, but Joker could probably be replaced with a regular thug and have nothing change. Same deal with the final Joker sequence in Knight.
APC's (Knight): They have a health bar, but act more like regular enemies the more you encounter them.
Deacon Blackfire (Knight): You don't fight him, just a bunch of goons. Different from Joker's Funhouse, because he actively participates in the fight.
Final Sequence (Knight): Just like Origins Joker, it's an interactive cutscene. I love the sequence, but there's no way to lose, and you aren't fighting anything. You're just running through a maze as Batman statues occasionally appear. And the final Joker beatdown could be replaced by a basic thug, so it doesn't count.
That should be all, but I'm sure there's more somewhere.