I get what you are trying to say but the key difference is "intent". Cavani was saying "thanks..." and used an anachronistic term as the second word. This word does have a different usage in some parts of the world and Cavani can claim some degree of ignorance about how a Direct translation of that term could be misinterpreted. He also felt he had been treated as harshly as those who had used such terms in a much more negative context.
As a older white male if I said "thanks blood" to a black man passing me my drink in a crowd it would be naff, uncomfortable, maybe a bit stereotyping but not outright offensive. However if I had been listing to a lot of rap music and said "Thanks my N....." then I would be totally in the wrong and would apologise. I could use the "cultural excuse" that I had been listening to rap music and used the term in an inappropriate way etc, but it still wouldn't excuse using the term.
Arnautovic used the N word on a number of occasions against opposition players to intimidate and belittle them. There are also cases of him hassling the women's players at West Ham and disrupting their training. Disrupting another teams training is definitely unprofessional and potentially threatening or predatory behaviour.
Will a future Ukraine vs Russia football game in a few years be a spicy affair with a lot of anger, taunts and tackles flying in...probably. But that is a different from intimidating and threatening players with racial taunts, It is racial hatred and should play no part in the modern game.
I'm relieved we seem to have pulled back from this moment of madness, but my god the club shouldn't be like a 4 year old at a bowling alley, needing the fans to act as some sort of moral conscience to keep them on the straight and narrow!