The lethality of the weapons in CoD games along with the importance of killstreaks does not eliminate the skill gap, it simply emphasizes map and match flow knowledge over individual encounter tactics. If being a pro in Halo means being able to effectively pair and use weapons for the situation, then being a pro in CoD means knowing when and where your enemies are likely to be.
It's ridiculous to claim that CoD has no skill gap. You are silly.
This is very true, in my severely limited experience. I played a few hours of Black Ops (1) multiplayer, and I was getting K/D scores like 1-2:30 the entire time. Then, my nephew sat down with me for around 90 minutes, and took me on a tour of the 4 or 5 most common multiplayer maps, showing me where people liked to run or camp, hidden angles you were exposed to when you ran through certain parts, how sections of the maps were connected to each other, all that kind of stuff.
I still sucked after, but I immediately went up to around 5:15, without changing anything else about how I was playing.