The "hardcore X-box phreak" is just jealous that he got used to the inferior input. On the other hand, he doesn't have to feel bad about it. If he is skilled, he should be able to get used to KB+M anyways.
Here is my argument. It is somewhat similar to yours. Turn speed is slower with DA, even if you ajust sensitivity, the controls will always have slower turn speed than KB+M and be more sturdy.
With KB+M you can adjust sensitivity so that you can turn very fact, but in turn, with high sensitivity you have to be more skilled to keep your aim steady. This means higher skill required gives higher reward since you have to have good reaction time and a steady aim.
With DA, this is no problem, you have automatically a steady aim wich removes skill factor but makes it easier to play. It also makes the game more about placement wich can make it more cerebral and good for slower players. DA is therefore a good choice for casual friendly FPS playing, while KB+M is better for fact-paced adrenalin filled competitive or semi-competitive games, (in this case I define competitive as players wanting their skill measured).
Would your friend listen to this argument? It seams like someone that agues "More precise input=H4xx0rz" wouln't take the time to listen to a well thought out argument.
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Essay Pro