So why do people want low kill times

The skill in Halo was landing headshots which killed faster, you could outplay your opponents with better aim. A less skilled player would aim for the body, get outplayed by the high skilled player who landed headshots.

You still had snipers in Halo that would one bullet kill with a headshot, they required twitch skills. A normal gunfight would came down to which player could stay on target, hit the most headshots while staffing and that takes skill. A game like Halo had a very high skill ceiling.