The darkness did clearly affect Rumple, no denying that but look at the degrees. You called Rumple ruthless but I strongly disagree with that, especially in terms of Rumple vs Hook. After the initial taking on of the DO’s curse and the first few months, Rumple did not murder anyone to our knowledge (you can speculate but canonically within the story, he did not). Instead he chose to make deals. He chose to give people what they wanted (or thought they wanted) in return for other favors. Yes, he manipulated the HECK out of people and situations but always played into what those people claimed to have wanted and always gave them a choice.
I am going to have to disagree that Rumpel didn’t murder people. The mute maid and cart guy six months after he became the dark one, Milah a few years after he became the dark one, Gepetto’s parents 60 years before curse, Cinderella’s fairy, Gaston, in the years right before the curse.
He also aught Cora and Regina both how to take a heart so that they could murder people. He brought that gypsy girl to Regina’s magic lesson, so Regina could murder her. He purposely taught Regina magic so that she would eventual become so evil that she would do the dark curse. He created the dark curse which was only cast through murder. He was going to torture and murder Robin Hood, but didn’t because Belle helped Robin escape and begged Rumpel not to murder him. We see Rumpel in the flashbacks few an far between, but he has done his share of murdering throughout history.
Rumpel doesn’t get a pass for helping other people to do evil just because they wanted it. That doesn’t make it not partially his fault too, doing bad deals was still wrong, especially when he knew that they would lead to someone being murdered or cursed or separated from their loved ones. That doesn’t make Hook good or better, but Rumpel wasn’t a nice guy either.