I think some people are just frustrated that the majority of the new cool weapons/ashes are locked behind difficult content. If you are too rusty to clear the initial difficulty wall, you'd be restricted to very little stuff after buying the $50 dlc.
That being said, a castle skip already exists so you can go collect the Smithscript series and Anvil Hammer - without killing a thing - as long as you explore hard enough!
Point being they beat Mohg ages ago and now rusty to play DLC.
Mohg is insanely weak to bloodflame too, I had much more problem with Blackgaol and Rellana early bosses then I did with Mohg while speedrunning a new chara into DLC map.
Mogh is like, one of the hardest bosses. I had more trouble with him than the final few bosses of the story, Godfrey and Radagon and their subsequent phases.
Don't know why you're getting downvoted, but yeah he's probably the worst boss in the game if you're running defensive builds or are used to backrolling attacks. Mohg is sooo much easier when using aggressive builds + rolling forwards or to his right though.
What is a difficult boss for your build can be a super easy boss for someone else's build.
First time I beat malenia I didn't understand what people were talking about. She was so easy. Because my build poise broke her non stop and I could essentially stun lock her to death. (Lv 150)
Wasn't until I played against her on my second character that I understood what a monumental challenge she can be.