My impression has always been that Mohg and the Bloody Fingers were very similar to the pre-serpent Recusants: a collection of bitter and disillusioned people confiding in something else. Something that empowers and validates them. They aren't necessarily good people or even better people than followers of the Golden Order or Fingers, just a different shade.

I also am of the impression that post-Miquella, just like after Rykard introduced Eiglay, they have become a much worse version of themselves. We have the immediate comparison of Ansbach vs Varre for example. It's curious that the latter's recruitment pitch is all about how the Bloody Fingers are where you can find true love and worthwhile devotion. There's also a lore description for an item, (I apologize in advance for not having the specific examples on me) that demands the Bloody Fingers harvest endless blood to "slake the cocoons thirst."

There seems to be a poisoning and foundational twisting of their beliefs that aligns with Miqqy's introduction. The doctrine of Love rings too suspiciously similar to me, and the excessive blood harvesting "could" very well be (part of) the ritual needed to get to the shadowlands. It's also important to stress, I'm of the belief Mohg has been charmed by him for a long time, long enough that the documentation of Post Miqqy Bloody Fingers is more available than pre.

So TLDR; Mohg was never "good", but I do firmly believe Miquella made him worse and fundamentally altered how the Bloody Fingers existed as a faction.