Here's how I see it, it takes "different" skill but not more. Those who say it does should do some gameplay and actually research it. Halo 3 I think it's 30-40% skill and the rest PURE luck with spawning and timing. Also your weapon over theirs.
COD I think is just camping and one shotting. COD is not really skill, but advantage. A 5 star general has way more perks than a recruit or a colonel so if it came down to it a general" with more exp" would easily win just from a couple little perks, not really skill.
However if a recruit did beat a general then I would put that into the skill category of COD.
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I haven't played H3 in a long time so I don't really know what it's like today, but when I did I had a negative KD and couldn't get past 40. I'm currently holding a 2+ KD in MW3 and at least a 1.5 in both MW2 and COD4. I'd say that about explains things. Keep in mind that COD does require some skill to play due to the myriad of weapons that can 1 hit kill, but Halo takes a little more. More than anything it takes teamwork, which is something that the COD franchise has never promoted.