U dont seem to have read my final sentence there, but oh nvm...You actually aren't saying anything different from what I was in a way that wasn't contradictory to yourself. Garp's mental state, no matter what it is, wouldn't stop him from neg diffing Luffy, and yet that's exactly what happened. That's exactly what the bolded part means you're saying.
The comparison is fair because it displays two scenarios where someone, despite being clearly stronger than the someone else, ended up being struck by that person because of their emotions affecting their mental state with both attacks being too weak to actually damage the person significantly.
Doffy killed his father and brother, yes, but that doesn't mean he didn't feel anything while doing so. His expression while killing Rocinante clearly displayed that the ordeal had an emotional effect on him. He wants to brutally kill Law, but he also commented that it was a shame he had to do so, meaning he'd prefer if he didn't have to do so. He said he thought of Law as though he were like his little brother. These mean emotional attachments, regardless of how unmerciful and vengeful Doffy is. No way around that. This obviously isn't petty shit to Doffy, otherwise he wouldn't be so upset about it. You're using the term petty shit to describe all that's happening now because Doffy used that to describe what happened in Dressrosa ten years ago, evoking a sense of familiarity to those who read your post to try and force pseudo-agreement because it gives off a sense of ¨That sounds right¨ due to the familiarity, but I digress.
The mental state is completely different, in one case is the mental state of love and afraid of losing someone u love in the other is sheer anger for getting betrayed by a man that once worked under him in case of betrayal he killed his brother and because of his misfortunes he killed his father what makes u think he still hold attachment's to law after all this? And no garp and luffy may have been far cry in terms of power but not doffy and law, Oda isnt going to give us the final fight of the arc a doffy who isnt at full power because of mental state, he actually want's to massacre them for destroying the country he's been residing in for 10 years.
My point still stand's the guy is in a bloodlusted state where he could kill anyone in cold blood, He may have a bit of attachment to his brother an father but then again he killed them without a second thought, and especially in this case considering what law has done to him, a bloodlust'ed character should be stronger and more aggressive in the fight but instead he is giving a sloppy display against law, my point still stand's that this isnt a case of mental state for the poor fight dofla is giving this just tells his limits as a fighter.